U.S. patent application number 14/885881 was filed with the patent office on 2016-04-21 for method and apparatus for uplink channel access in a high efficiency wireless lan.
The applicant listed for this patent is NEWRACOM, INC.. Invention is credited to Yongho SEOK.
Application Number | 20160113034 14/885881 |
Document ID | / |
Family ID | 55750197 |
Filed Date | 2016-04-21 |
United States Patent
Application |
20160113034 |
Kind Code |
A1 |
SEOK; Yongho |
April 21, 2016 |
METHOD AND APPARATUS FOR UPLINK CHANNEL ACCESS IN A HIGH EFFICIENCY
WIRELESS LAN
Abstract
The present disclosure relates to a method and apparatus for
uplink channel access in a High Efficiency WLAN (HEW). According to
one aspect, a method for transmitting an uplink frame by a station
(STA) to an access point (AP) in a wireless local area network may
be provided. The method may include receiving from the AP a trigger
frame for eliciting an uplink transmission from the STA,
transmitting to the AP the uplink frame according to a type of the
trigger frame, wherein when the uplink frame is transmitted in an
uplink multiple user (MU) transmission, the uplink frame includes a
padding added by the STA such that transmissions from a plurality
of STAs including the STA in the uplink MU transmission end at a
same time indicated by the trigger frame, and receiving from the AP
a frame in response to the uplink MU transmission a predetermined
time after an end of the uplink MU transmission.
Inventors: |
SEOK; Yongho; (Irvine,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEWRACOM, INC. |
Irvine |
CA |
US |
|
|
Family ID: |
55750197 |
Appl. No.: |
14/885881 |
Filed: |
October 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62064785 |
Oct 16, 2014 |
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62069662 |
Oct 28, 2014 |
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62083855 |
Nov 24, 2014 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 84/12 20130101;
H04W 74/04 20130101 |
International
Class: |
H04W 74/04 20060101
H04W074/04 |
Claims
1. A method for transmitting an uplink frame by a station (STA) to
an access point (AP) in a wireless local area network, the method
comprising: receiving from the AP a trigger frame for eliciting an
uplink transmission from the STA; transmitting to the AP the uplink
frame according to a type of the trigger frame, wherein when the
uplink frame is transmitted in an uplink multiple user (MU)
transmission, the uplink frame includes a padding added by the STA
such that transmissions from a plurality of STAs including the STA
in the uplink MU transmission end at a same time indicated by the
trigger frame; and receiving from the AP a frame in response to the
uplink MU transmission a predetermined time after an end of the
uplink MU transmission.
2. The method according to claim 1, wherein a length of the padding
is determined based on information on a transmission time of the
uplink MU transmission included in the trigger frame.
3. The method according to claim 1, wherein the STA receives the
frame in response to the uplink MU transmission a SIFS (Short
Inter-Frame Space) time after the end of the uplink MU
transmission.
4. The method according to claim 1, wherein the frame received in
response to the uplink MU transmission includes acknowledgment
(ACK) information for the uplink MU transmission.
5. The method according to claim 4, wherein the AP determines that
the uplink MU transmission is successfully received, when the AP
receives an uplink frame from at least one STA among the plurality
of STAs.
6. The method according to claim 5, wherein the frame including the
ACK information is transmitted by the AP, when a physical layer of
the AP indicates that an uplink frame from at least one STA among
the plurality of STAs is received with no error.
7. The method according to claim 1, wherein the frame received in
response to the uplink MU transmission includes another trigger
frame for eliciting another uplink MU transmission.
8. The method according to claim 7, wherein the STA transmits an
uplink frame in the another uplink MU transmission, when the frame
received in response to the uplink MU transmission includes another
trigger frame for eliciting another uplink MU transmission.
9. The method according to claim 1, wherein the frame received in
response to the uplink MU transmission includes ACK information for
the uplink MU transmission and another trigger frame for eliciting
another uplink MU transmission.
10. The method according to claim 1, wherein an ACK policy of the
STA is set to Immediate Block ACK.
11. The method according to claim 1, wherein ACK policies of the
plurality of STAs are set to a same value.
12. The method according to claim 1, wherein the trigger frame is
broadcast to elicit the uplink MU transmissions from unspecified
plurality of STAs, and the trigger frame includes response
condition information used by a STA receiving the trigger frame for
determining whether to transmit the uplink frame in response to the
trigger frame.
13. The method according to claim 12, wherein the response
condition information indicates that a Traffic Indication Map (TIM)
STA is allowed to transmit the uplink frame in response to the
trigger frame.
14. The method according to claim 13, wherein the uplink frame
transmitted by the STA that is a TIM STA indicates that the STA
requests a downlink frame for the STA buffered at the AP, the frame
received in response to the uplink MU transmission includes the
downlink frame for the STA buffered at the AP, and the downlink
frame is included in a downlink MU Physical layer Protocol Data
Unit (PPDU).
15. The method according to claim 12, wherein the response
condition information indicates that a STA having an uplink traffic
having a specific access category is allowed to transmit the uplink
frame in response to the trigger frame.
16. The method according to claim 1, wherein the STA checks a
network allocation vector (NAV) before transmitting the uplink
frame, and transmits the uplink frame when a channel is idle
according to the NAV.
17. The method according to claim 1, the STA transmits the uplink
frame including a control frame in the uplink MU transmission when
the type of the trigger frame is a first type.
18. The method according to claim 1, the STA transmits the uplink
frame including a control frame in an uplink single user (SU)
transmission when the type of the trigger frame is a second
type.
19. The method according to claim 1, the STA transmits the uplink
frame including a data frame in the uplink MU transmission when the
type of the trigger frame is a third type.
20. A method for receiving an uplink transmission by an access
point (AP) in a wireless local area network, the method comprising:
transmitting a trigger frame for eliciting the uplink transmission
from one or more STAs; receiving from the one or more STAs the
uplink transmission according to a type of the trigger frame,
wherein when the uplink transmission is an uplink multiple user
(MU) transmission, each of at least one uplink frame includes a
padding added by a STA of a plurality of STAs such that
transmissions from the plurality of STAs in the uplink MU
transmission end at a same time indicated by the trigger frame; and
transmitting a frame in response to the uplink MU transmission a
predetermined time after an end of the uplink MU transmission.
Description
[0001] This application claims the benefits of U.S. Provisional
Application No. 62/064,785, filed on Oct. 16, 2014, U.S.
Provisional Application No. 62/069,662, filed on Oct. 28, 2014, and
U.S. Provisional Application No. 62/083,855, filed on Nov. 24,
2014, which are hereby incorporated by reference as if fully set
forth herein.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates to a Wireless Local Area
Network (WLAN), and more particularly, to a method, apparatus, and
software for uplink channel access in a High Efficiency WLAN (HEW),
and a recording medium that stores the software.
[0004] 2. Related Art
[0005] Along with the recent development of information and
telecommunication technology, various wireless communication
techniques have been developed. Among them, the WLAN enables a user
to wirelessly access the Internet based on radio frequency
technology in a home, an office, or a specific service area using a
portable terminal such as a Personal Digital Assistant (PDA), a
laptop computer, a Portable Multimedia Player (PMP), a smartphone,
etc.
[0006] To overcome limitations in communication speed that the WLAN
faces, the recent technical standards have introduced a system that
increases the speed, reliability, and coverage of a wireless
network. For example, the Institute of Electrical and Electronics
Engineers (IEEE) 802.11n standard has introduced Multiple Input
Multiple Output (MIMO) that is implemented using multiple antennas
at both a transmitter and a receiver in order to support High
Throughput (HT) at a data processing rate of up to 540 Mbps,
minimize transmission errors, and optimize data rates.
[0007] In recent times, to support increased numbers of devices
supporting WLAN, such as smartphones, more Access Points (APs) have
been deployed. Despite increase in use of WLAN devices supporting
the Institute of Electrical and Electronics Engineers (IEEE)
802.11ac standard, that provide high performance relative to WLAN
devices supporting the legacy IEEE 802.11g/n standard, a WLAN
system supporting higher performance is required due to WLAN users'
increased use of high volume content such as a ultra high
definition video. Although a conventional WLAN system has aimed at
increase of bandwidth and improvement of a peak transmission rate,
actual users thereof could not feel drastic increase of such
performance.
[0008] In a task group called IEEE 802.11ax, High Efficiency WLAN
(HEW) standardization is under discussion. The HEW aims at
improving performance felt by users demanding high-capacity,
high-rate services while supporting simultaneous access of numerous
stations in an environment in which a plurality of APs is densely
deployed and coverage areas of APs overlap.
[0009] However, there is no specified method for uplink channel
access in a HEW.
SUMMARY
[0010] Objects of the present disclosure is to provide a method and
apparatus for uplink channel access in a High Efficiency WLAN
(HEW).
[0011] The objects of the present disclosure are not limited to the
foregoing descriptions, and additional objects will become apparent
to those having ordinary skill in the pertinent art to the present
disclosure based upon the following descriptions.
[0012] In an aspect of the present disclosure, a method for
transmitting an uplink frame by a station (STA) to an access point
(AP) in a wireless local area network may be provided. The method
may include receiving from the AP a trigger frame for eliciting an
uplink transmission from the STA, transmitting to the AP the uplink
frame according to a type of the trigger frame, wherein when the
uplink frame is transmitted in an uplink multiple user (MU)
transmission, the uplink frame includes a padding added by the STA
such that transmissions from a plurality of STAs including the STA
in the uplink MU transmission end at a same time indicated by the
trigger frame, and receiving from the AP a frame in response to the
uplink MU transmission a predetermined time after an end of the
uplink MU transmission.
[0013] In another aspect of the present disclosure, a method for
receiving an uplink transmission by an AP in a wireless local area
network may be provided. The method may include transmitting a
trigger frame for eliciting the uplink transmission from one or
more STAs, receiving from the one or more STAs the uplink
transmission according to a type of the trigger frame, wherein when
the uplink transmission is an uplink MU transmission, each of at
least one uplink frame includes a padding added by a STA of a
plurality of STAs such that transmissions from the plurality of
STAs in the uplink MU transmission end at a same time indicated by
the trigger frame, and transmitting a frame in response to the
uplink MU transmission a predetermined time after an end of the
uplink MU transmission.
[0014] In another aspect of the present disclosure, an STA
apparatus for transmitting an uplink frame to an AP in a wireless
local area network may be provided. The STA apparatus may include a
baseband processor, a Radio Frequency (RF) transceiver, a memory,
etc. The baseband processor may be configured to receive from the
AP a trigger frame for eliciting an uplink transmission from the
STA using the transceiver, to transmit to the AP the uplink frame
according to a type of the trigger frame using the transceiver,
wherein when the uplink frame is transmitted in an uplink MU
transmission, the uplink frame includes a padding added by the STA
such that transmissions from a plurality of STAs including the STA
in the uplink MU transmission end at a same time indicated by the
trigger frame, and to receive from the AP a frame using the
transceiver in response to the uplink MU transmission a
predetermined time after an end of the uplink MU transmission.
[0015] In another aspect of the present disclosure, an AP apparatus
for receiving an uplink transmission in a wireless local area
network may be provided. The AP apparatus may include a baseband
processor, an RF transceiver, a memory, etc. The baseband processor
may be configured to transmit a trigger frame for eliciting the
uplink transmission from one or more STAs using the transceiver, to
receive from the one or more STAs the uplink transmission according
to a type of the trigger frame using the transceiver, wherein when
the uplink transmission is an uplink MU transmission, each of at
least one uplink frame includes a padding added by a STA of a
plurality of STAs such that transmissions from the plurality of
STAs in the uplink MU transmission end at a same time indicated by
the trigger frame, and to transmit a frame in response to the
uplink MU transmission using the transceiver a predetermined time
after an end of the uplink MU transmission.
[0016] In another aspect of the present disclosure, a software or
computer-readable medium having instructions executable for an STA
to transmit an uplink frame to an AP in a wireless local area
network may be provided. The executable instructions may cause the
STA to receive from the AP a trigger frame for eliciting an uplink
transmission from the STA to transmit to the AP the uplink frame
according to a type of the trigger frame, wherein when the uplink
frame is transmitted in an uplink MU transmission, the uplink frame
includes a padding added by the STA such that transmissions from a
plurality of STAs including the STA in the uplink MU transmission
end at a same time indicated by the trigger frame, and to receive
from the AP a frame in response to the uplink MU transmission a
predetermined time after an end of the uplink MU transmission.
[0017] In another aspect of the present disclosure, a software or
computer-readable medium having instructions executable for an AP
to receive an uplink transmission in a wireless local area network
may be provided. The executable instructions may cause the AP a
memory, etc. The baseband processor may be configured to transmit a
trigger frame for eliciting the uplink transmission from one or
more STAs, to receive from the one or more STAs the uplink
transmission according to a type of the trigger frame, wherein when
the uplink transmission is an uplink MU transmission, each of at
least one uplink frame includes a padding added by a STA of a
plurality of STAs such that transmissions from the plurality of
STAs in the uplink MU transmission end at a same time indicated by
the trigger frame, and to transmit a frame in response to the
uplink MU transmission a predetermined time after an end of the
uplink MU transmission.
[0018] It is to be understood that both the foregoing summarized
features are exemplary aspects of the following detailed
description of the present disclosure without limiting the scope of
the present disclosure.
[0019] According to the present disclosure, a method and apparatus
for uplink channel access in a HEW can be provided.
[0020] The advantages of the present disclosure are not limited to
the foregoing descriptions, and additional advantages will become
apparent to those having ordinary skill in the pertinent art to the
present disclosure based upon the following descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The accompanying drawings, which are included to provide a
further understanding of the disclosure and are incorporated in and
constitute a part of this application, illustrate embodiment(s) of
the disclosure and together with the description serve to explain
the principle of the disclosure. In the drawings:
[0022] FIG. 1 is a block diagram of a Wireless Local Area Network
(WLAN) device;
[0023] FIG. 2 is a schematic block diagram of an exemplary
transmitting signal processing unit in a WLAN;
[0024] FIG. 3 is a schematic block diagram of an exemplary
receiving signal processing unit in a WLAN;
[0025] FIG. 4 depicts a relationship between InterFrame Spaces
(IFSs);
[0026] FIG. 5 is a conceptual diagram illustrating a procedure for
transmitting a frame in Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA) for avoiding collisions between
frames in a channel;
[0027] FIG. 6 depicts an exemplary frame structure in a WLAN
system;
[0028] FIG. 7 depicts an exemplary HE PPDU frame format.
[0029] FIG. 8 depicts an exemplary High Efficiency (HE) Physical
layer Protocol Data Unit (PPDU) frame format according to the
present disclosure;
[0030] FIG. 9 depicts subchannel allocation in a HE PPDU frame
format according to the present disclosure;
[0031] FIG. 10 depicts a subchannel allocation method according to
the present disclosure;
[0032] FIG. 11 depicts the starting and ending points of an High
Efficiency Long Training Field (HE-LTF) field in a HE PPDU frame
format according to the present disclosure;
[0033] FIG. 12 depicts a High Efficiency SIGnal B (HE-SIG-B) field
and a High Efficiency SIGnal C (HE-SIG-C) field in the HE PPDU
frame format according to the present disclosure;
[0034] FIG. 13 depicts another example of a HE PPDU frame format
according to the present disclosure;
[0035] FIGS. 14 to 17 depict exemplary frame exchange sequences
each including Uplink (UL) Multi-User (MU) transmission according
to the present disclosure;
[0036] FIGS. 18 and 19 depict exemplary exchanges of a UL MU Poll
Request frame, a UL MU Poll Response frame, and a UL MU Poll
Confirm frame according to the present disclosure;
[0037] FIG. 20 depicts UL MU random access of Stations (STAs)
operating in power save mode according to the present
disclosure;
[0038] FIG. 21 depicts Access Category (AC)-based UL MU random
access according to the present disclosure;
[0039] FIG. 22 depicts an exemplary trigger type-based UL
transmission scheme according to the present disclosure;
[0040] FIG. 23 depicts an exemplary method according to the present
disclosure; and
[0041] FIG. 24 depicts another exemplary method according to the
present disclosure.
DETAILED DESCRIPTION
[0042] In the following detailed description, only certain
embodiments of the present disclosure have been shown and
described, simply by way of illustration. As those skilled in the
art would realize, the described embodiments may be modified in
various different ways, all without departing from the spirit or
scope of the present disclosure. Accordingly, the drawings and
description are to be regarded as illustrative in nature and not
restrictive. Like reference numerals designate like elements
throughout the specification.
[0043] In a Wireless Local Area network (WLAN), a Basic Service Set
(BSS) includes a plurality of WLAN devices. A WLAN device may
include a Medium Access Control (MAC) layer and a PHYsical (PHY)
layer according to Institute of Electrical and Electronics
Engineers (IEEE) 802.11 series standards. In the plurality of WLAN
devices, at least one the WLAN device may be an Access Point (AP)
and the other WLAN devices may be non-AP Stations (non-AP STAs).
Alternatively, all of the plurality of WLAN devices may be non-AP
STAs in an ad-hoc networking environment. In general, AP STA and
non-AP STA may be each referred to as a STA or may be collectively
referred to as STAs. However, for ease of description herein, only
the non-AP STAs may be referred to herein as the STAs.
[0044] FIG. 1 is a block diagram of a WLAN device.
[0045] Referring to FIG. 1, a WLAN device 1 includes a baseband
processor 10, a Radio Frequency (RF) transceiver 20, an antenna
unit 30, a memory 40, an input interface unit 50, an output
interface unit 60, and a bus 70.
[0046] The baseband processor 10 may be simply referred to as a
processor, performs baseband signal processing described in the
present specification, and includes a MAC processor (or MAC entity)
11 and a PHY processor (or PHY entity) 15.
[0047] In an embodiment of the present disclosure, the MAC
processor 11 may include a MAC software processing unit 12 and a
MAC hardware processing unit 13. The memory 40 may store software
(hereinafter referred to as `MAC software`) including at least some
functions of the MAC layer. The MAC software processing unit 12 may
execute the MAC software to implement some functions of the MAC
layer, and the MAC hardware processing unit 13 may implement the
remaining functions of the MAC layer in hardware (hereinafter
referred to as `MAC hardware`). However, the MAC processor 11 is
not limited to the foregoing implementation examples.
[0048] The PHY processor 15 includes a transmitting (TX) signal
processing unit 100 and a receiving (RX) signal processing unit
200.
[0049] The baseband processor 10, the memory 40, the input
interface unit 50, and the output interface unit 60 may communicate
with one another via the bus 70.
[0050] The RF transceiver 20 includes an RF transmitter 21 and an
RF receiver 22.
[0051] The memory 40 may further store an Operating System (OS) and
applications. The input interface unit 50 receives information from
a user, and the output interface unit 60 outputs information to the
user.
[0052] The antenna unit 30 includes one or more antennas. When
Multiple input Multiple Output (MIMO) or Multi-User MIMO (MU-MIMO)
is used, the antenna unit 30 may include a plurality of
antennas.
[0053] FIG. 2 is a schematic block diagram of an exemplary
transmission signal processor in a WLAN.
[0054] Referring to FIG. 2, the transmitting signal processing unit
100 may include an encoder 110, an interleaver 120, a mapper 130,
an Inverse Fourier Transformer (IFT) 140, and a Guard Interval (GI)
inserter 150.
[0055] The encoder 110 encodes input data. For example, the encoder
110 may be a Forward Error Correction (FEC) encoder. The FEC
encoder may include a Binary Convolutional Code (BCC) encoder
followed by a puncturing device, or the FEC encoder may include a
Low-Density Parity-Check (LDPC) encoder.
[0056] The transmitting signal processing unit 100 may further
include a scrambler for scrambling the input data before encoding
to reduce the probability of long sequences of 0s or 1s. If BCC
encoding is used in the encoder 110, the transmitting signal
processing unit 100 may further include an encoder parser for
demultiplexing the scrambled bits among a plurality of BCC
encoders. If LDPC encoding is used in the encoder 110, the
transmitting signal processing unit 100 may not use the encoder
parser.
[0057] The interleaver 120 interleaves the bits of each stream
output from the encoder 110 to change the order of bits.
Interleaving may be applied only when BCC encoding is used in the
encoder 110. The mapper 130 maps the sequence of bits output from
the interleaver 120 to constellation points. If LDPC encoding is
used in the encoder 110, the mapper 130 may further perform LDPC
tone mapping in addition to constellation mapping.
[0058] When MIMO or MU-MIMO is used, the transmitting signal
processing unit 100 may use a plurality of interleavers 120 and a
plurality of mappers 130 corresponding to the number of spatial
streams, N.sub.SS. In this case, the transmitting signal processing
unit 100 may further include a stream parser for dividing outputs
of the BCC encoders or output of the LDPC encoder into blocks that
are sent to different interleavers 120 or mappers 130. The
transmitting signal processing unit 100 may further include a
Space-Time Block Code (STBC) encoder for spreading the
constellation points from the N.sub.SS spatial streams into
N.sub.STS space-time streams and a spatial mapper for mapping the
space-time streams to transmit chains. The spatial mapper may use
direct mapping, spatial expansion, or beamforming.
[0059] The IFT 140 converts a block of constellation points output
from the mapper 130 or the spatial mapper to a time-domain block
(i.e., a symbol) by using Inverse Discrete Fourier Transform (IDFT)
or Inverse Fast Fourier Transform (IFFT). If the STBC encoder and
the spatial mapper are used, the IFT 140 may be provided for each
transmit chain.
[0060] When MIMO or MU-MIMO is used, the transmitting signal
processing unit 100 may insert Cyclic Shift Diversities (CSDs) to
prevent unintentional beamforming. The CSD insertion may occur
before or after IFT. The CSD may be specified per transmit chain or
may be specified per space-time stream. Alternatively, the CSD may
be applied as a part of the spatial mapper.
[0061] When MU-MIMO is used, some blocks before the spatial mapper
may be provided for each user.
[0062] The GI inserter 150 prepends a GI to the symbol. The
transmitting signal processing unit 100 may optionally perform
windowing to smooth edges of each symbol after inserting the GI.
The RF transmitter 21 converts the symbols into an RF signal and
transmits the RF signal via the antenna unit 30. When MIMO or
MU-MIMO is used, the GI inserter 150 and the RF transmitter 21 may
be provided for each transmit chain.
[0063] FIG. 3 is a schematic block diagram of an exemplary a
receiving signal processor in a WLAN.
[0064] Referring to FIG. 3, the receiving signal processing unit
200 includes a GI remover 220, a Fourier Transformer (FT) 230, a
demapper 240, a deinterleaver 250, and a decoder 260.
[0065] An RF receiver 22 receives an RF signal via the antenna unit
30 and converts the RF signal into symbols. The GI remover 220
removes the GI from the symbol. When MIMO or MU-MIMO is used, the
RF receiver 22 and the GI remover 220 may be provided for each
receive chain.
[0066] The FT 230 converts the symbol (i.e., the time-domain block)
into a block of constellation points by using a Discrete Fourier
Transform (DFT) or a Fast Fourier Transform (FFT). The FT 230 may
be provided for each receive chain.
[0067] When MIMO or MU-MIMO is used, the receiving signal
processing unit 200 may include a spatial demapper for converting
Fourier Transformed receiver chains to constellation points of the
space-time streams, and an STBC decoder for despreading the
constellation points from the space-time streams into the spatial
streams.
[0068] The demapper 240 demaps the constellation points output from
the FT 230 or the STBC decoder to bit streams. If LDPC encoding is
applied to the received signal, the demapper 240 may further
perform LDPC tone demapping before constellation demapping. The
deinterleaver 250 deinterleaves the bits of each stream output from
the demapper 240. Deinterleaving may be applied only when a BCC
encoding scheme is applied to the received signal.
[0069] When MIMO or MU-MIMO is used, the receiving signal
processing unit 200 may use a plurality of demappers 240 and a
plurality of deinterleavers 250 corresponding to the number of
spatial streams. In this case, the receiving signal processing unit
200 may further include a stream deparser for combining streams
output from the deinterleavers 250.
[0070] The decoder 260 decodes the streams output from the
deinterleaver 250 or the stream deparser. For example, the decoder
100 may be an FEC decoder. The FEC decoder may include a BCC
decoder or an LDPC decoder. The receiving signal processing unit
200 may further include a descrambler for descrambling the decoded
data. If BCC decoding is used in the decoder 260, the receiving
signal processing unit 200 may further include an encoder deparser
for multiplexing the data decoded by a plurality of BCC decoders.
If LDPC decoding is used in the decoder 260, the receiving signal
processing unit 200 may not use the encoder deparser.
[0071] In a WLAN system, Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA) is a basic MAC access mechanism. The
CSMA/CA mechanism is referred to as Distributed Coordination
Function (DCF) of IEEE 802.11 MAC, shortly as a `listen before
talk` access mechanism. According to the CSMA/CA mechanism, an AP
and/or a STA may sense a medium or a channel for a predetermined
time before starting transmission, that is, may perform Clear
Channel Assessment (CCA). If the AP or the STA determines that the
medium or channel is idle, it may start to transmit a frame on the
medium or channel. On the other hand, if the AP and/or the STA
determines that the medium or channel is occupied or busy, it may
set a delay period (e.g., a random backoff period), wait for the
delay period without starting transmission, and then attempt to
transmit a frame. By applying a random backoff period, a plurality
of STAs are expected to attempt frame transmission after waiting
for different time periods, resulting in minimizing collisions.
[0072] FIG. 4 depicts a relationship between InterFrame Spaces
(IFSs).
[0073] WLAN devices may exchange data frames, control frames, and
management frames with each other.
[0074] A data frame is used for transmission of data forwarded to a
higher layer. The WLAN device transmits the data frame after
performing backoff if a Distributed Coordination Function IFS
(DIFS) has elapsed from a time when the medium has been idle. A
management frame is used for exchanging management information
which is not forwarded to the higher layer. The WLAN device
transmits the management frame after performing backoff if an IFS
such as the DIFS or a Point Coordination Function IFS (PIFS) has
elapsed. Subtype frames of the management frame include a beacon
frame, an association request/response frame, a probe
request/response frame, and an authentication request/response
frame. A control frame is used for controlling access to the
medium. Subtype frames of the control frame include a
Request-To-Send (RTS) frame, a Clear-To-Send (CTS) frame, and an
ACKnowledgement (ACK) frame. In the case that the control frame is
not a response frame to another frame, the WLAN device transmits
the control frame after performing backoff if the DIFS has elapsed.
In case that the control frame is a response frame to another
frame, the WLAN device transmits the control frame without
performing backoff if a Short IFS (SIFS) has elapsed. The type and
subtype of a frame may be identified by a type field and a subtype
field in a Frame Control (FC) field.
[0075] On the other hand, a Quality of Service (QoS) STA transmits
a frame after performing backoff if an Arbitration IFS (AIFS) for
an associated Access Category (AC), i.e., AIFS[i] (i is determined
based on AC) has elapsed. In this case, the AIFC[i] may be used for
a data frame, a management frame, or a control frame that is not a
response frame.
[0076] In the example illustrated in FIG. 4, upon generation of a
frame to be transmitted, a STA may transmit the frame immediately,
if it determines that the medium is idle for the DIFS or AIFS[i] or
longer. The medium is busy for a time period during which the STA
transmits the frame. During the time period, upon generation of a
frame to be transmitted, another STA may defer access by confirming
that the medium is busy. If the medium gets idle, the STA that
intends to transmit the frame may perform a backoff operation after
a predetermined IFS in order to minimize collision with any other
STA. Specifically, the STA that intends to transmit the frame
selects a random backoff count, waits for a slot time corresponding
to the selected random backoff count, and then attempt
transmission. The random backoff count is determined based on a
Contention Window (CW) parameter and the medium is monitored
continuously during count-down of backoff slots (i.e. decrement a
backoff count-down) according to the determined backoff count. If
the STA monitors the medium as busy, the STA discontinues the
count-down and waits, and then, if the medium gets idle, the STA
resumes the count-down. If the backoff slot count reaches 0, the
STA may transmit the next frame.
[0077] FIG. 5 is a conceptual diagram illustrating a CSMA/CA-based
frame transmission procedure for avoiding collisions between frames
in a channel.
[0078] Referring FIG. 5, a first STA (STA1) is a transmit WLAN
device for transmitting data, a second STA (STA2) is a receive WLAN
device for receiving the data from STA1, and a third STA (STA3) is
a WLAN device which may be located in an area where a frame
transmitted from STA1 and/or a frame transmitted from STA2 can be
received by STA3.
[0079] STA1 may determine whether the channel is busy by carrier
sensing. The STA1 may determine the channel occupation based on an
energy level on the channel or correlation of signals in the
channel, or may determine the channel occupation by using a Network
Allocation Vector (NAV) timer.
[0080] After determining that the channel is not being used by
other devices during DIFS (that is, the channel is idle), STA1 may
transmit an RTS frame to STA2 after performing backoff. Upon
receiving the RTS frame, STA2 may transmit a CTS frame as a
response to the CTS frame after SIFS.
[0081] When STA3 receives the RTS frame, STA3 may set the NAV timer
for a transmission duration of subsequently transmitted frame by
using duration information included in the RTS frame. For example,
the NAV timer may be set for a duration of SIFS+CTS frame
duration+SIFS+data frame duration+SIFS+ACK frame duration. When
STA3 receives the CTS frame, it may set the NAV timer for a
transmission duration of subsequently transmitted frames by using
duration information included in the CTS frame. For example, the
NAV timer may be set for a duration of SIFS+a data frame
duration+SIFS+an ACK frame duration. Upon receiving a new frame
before the NAV timer expires, STA3 may update the NAV timer by
using duration information included in the new frame. STA3 does not
attempt to access the channel until the NAV timer expires.
[0082] When STA1 receives the CTS frame from STA2, it may transmit
a data frame to STA2 after SIFS elapsed from the CTS frame has been
completely received. Upon successfully receiving the data frame,
STA2 may transmit an ACK frame as a response to the data frame
after SIFS elapsed.
[0083] When the NAV timer expires, STA3 may determine whether the
channel is busy through the use of carrier sensing. Upon
determining that the channel is not in use by other devices during
DIFS and after the NAV timer has expired, STA3 may attempt channel
access after a contention window after a random backoff has
elapsed.
[0084] FIG. 6 depicts an exemplary frame structure in a WLAN
system.
[0085] PHY layer may prepare a transmission MAC PDU (MPDU) in
response to an instruction (or a primitive, which is a set of
instructions or a set of parameters) by the MAC layer. For example,
upon receipt of an instruction requesting transmission start from
the MAC layer, the PHY layer may switch to a transmission mode,
construct a frame with information (e.g., data) received from the
MAC layer, and transmit the frame.
[0086] Upon detection of a valid preamble in a received frame, the
PHY layer monitors a header of the preamble and transmits an
instruction indicating reception start of the PHY layer to the MAC
layer.
[0087] Information is transmitted and received in frames in the
WLAN system. For this purpose, a Physical layer Protocol Data Unit
(PPDU) frame format is defined.
[0088] A PPDU frame may include a Short Training Field (STF) field,
a Long Training Field (LTF) field, a SIGNAL (SIG) field, and a Data
field. The most basic (e.g., a non-High Throughput (non-HT)) PPDU
frame may include only a Legacy-STF (L-STF) field, a Legacy-LTF
(L-LTF) field, a SIG field, and a Data field. Additional (or other
types of) STF, LTF, and SIG fields may be included between the SIG
field and the Data field according to the type of a PPDU frame
format (e.g., an HT-mixed format PPDU, an HT-greenfield format
PPDU, a Very High Throughput (VHT) PPDU, etc.).
[0089] The STF is used for signal detection, Automatic Gain Control
(AGC), diversity selection, fine time synchronization, etc. The LTF
field is used for channel estimation, frequency error estimation,
etc. The STF and the LTF fields may be referred to as signals for
OFDM PHY layer synchronization and channel estimation.
[0090] The SIG field may include a RATE field and a LENGTH field.
The RATE field may include information about a modulation scheme
and coding rate of data. The LENGTH field may include information
about the length of the data. The SIG field may further include
parity bits, SIG TAIL bits, etc.
[0091] The Data field may include a SERVICE field, a Physical layer
Service Data Unit (PSDU), and PPDU TAIL bits. When needed, the Data
field may further include padding bits. A part of the bits of the
SERVICE field may be used for synchronization at a descrambler of a
receiver. The PSDU corresponds to a MAC PDU defined at the MAC
layer and may include data generated/used in a higher layer. The
PPDU TAIL bits may be used to return an encoder to a zero state.
The padding bits may be used to match the length of the Data filed
in predetermined units.
[0092] A MAC PDU is defined according to various MAC frame formats.
A basic MAC frame includes a MAC header, a frame body, and a Frame
Check Sequence (FCS). The MAC frame includes a MAC PDU and may be
transmitted and received in the PSDU of the data part in the PPDU
frame format.
[0093] The MAC header includes a Frame Control field, a
Duration/Identifier (ID) field, an Address field, etc. The Frame
Control field may include control information required for frame
transmission/reception. The Duration/ID field may be set to a time
for transmitting the frame. For details of Sequence Control, QoS
Control, and HT Control subfields of the MAC header, refer to the
IEEE 802.11-2012 technical specification.
[0094] The Frame Control field of the MAC header may include
Protocol Version, Type, Subtype, To DS, From DS, More Fragment,
Retry, Power Management, More Data, Protected Frame, and Order
subfields. For the contents of each subfield in the Frame Control
field, refer to the IEEE 802.11-2012 technical specification.
[0095] A Null-Data Packet (NDP) frame format is a frame format that
does not include a data packet. In other words, the NDP frame
format includes only a Physical Layer Convergence Protocol (PLCP)
header part (i.e., the STF, LTF, and SIG fields) of the general
PPDU frame format, without the remaining part (i.e., the Data
field) of the general PPDU frame format. The NDP frame format may
be referred to as a short frame format.
[0096] The IEEE 802.11ax task group is discussing a WLAN system,
called a High Efficiency WLAN (HEW) system, that operates in 2.4
GHz or 5 GHz and supports a channel bandwidth (or channel width) of
20 MHz, 40 MHz, 80 MHz, or 160 MHz. The present disclosure defines
a new PPDU frame format for the IEEE 802.1 lax HEW system. The new
PPDU frame format may support MU-MIMO or OFDMA. A PPDU of the new
format may be referred to as a `HEW PPDU` or `HE PPDU` (similarly,
HEW xyz may be referred to as `HE xyz` or `HE-xyz` in the following
descriptions).
[0097] In present specification, the term `MU-MIMO or OFDMA mode`
includes MU-MIMO without using OFDMA, or OFDMA mode without using
MU-MIMO in an orthogonal frequency resource, or OFDMA mode using
MU-MIMO in an orthogonal frequency resource.
[0098] FIG. 7 depicts an exemplary HE PPDU frame format.
[0099] A transmitting STA may generate a PPDU frame according to
the HE PPDU frame format as illustrated in FIG. 7 and transmit the
PPDU frame to a receiving STA. The receiving STA may detect a PPDU
and then process the PPDU.
[0100] The HE PPDU frame format may broadly include two parts: the
first part including an L-STF field, an L-LTF field, an L-SIG
field, an RL-SIG field, a HE-SIG-A field, and a HE-SIG-B field and
the second part including a HE-STF field, a HE-LTF field, and a
HE-DATA field. 64-FFT based on a channel bandwidth of 20 MHz may be
applied to the first part and a basic subcarrier spacing of 312.5
kHz and a basic DFT period of 3.2 .mu.s may be included in the
first part. 256-FFT based on a channel bandwidth of 20 MHz may be
applied to the second part and a basic subcarrier spacing of 75.125
kHz and a basic DFT period of 12.8 .mu.s may be included in the
second part.
[0101] The HE-SIG-A field may include N.sub.HESIGA symbols, the
HE-SIG-B field may include N.sub.HESIGB symbols, the HE-LTF field
may include N.sub.HELTF symbols, and the HE-DATA field may include
N.sub.DATA symbols.
[0102] A detailed description of the fields included in the HE PPDU
frame format is given in Table 1.
TABLE-US-00001 TABLE 1 DFT Subcarrier Element definition duration
period GI spacing Description Legacy(L)- Non-high 8 .mu.s -- --
equivalent to L-STF of a non-trigger-based STF throughput(HT) 1,250
kHz PPDU has a periodicity of 0.8 .mu.s Short Training with 10
periods. field L-LTF Non-HT Long 8 .mu.s 3.2 .mu.s 1.6 .mu.s 312.5
kHz Training field L-SIG Non-HT 4 .mu.s 3.2 .mu.s 0.8 .mu.s 312.5
kHz SIGNAL field RL-SIG Repeated Non- 4 .mu.s 3.2 .mu.s 0.8 .mu.s
312.5 kHz HT SIGNAL field HE-SIG-A HE SIGNAL A N.sub.HESIGA * 3.2
.mu.s 0.8 .mu.s 312.5 kHz HE-SIG-A is duplicated on each field 4
.mu.s 20 MHz segment after the legacy preamble to indicate common
control information. N.sub.HESIGA means the number of OFDM symbols
of the HE-SIG-A field and is equal to 2 or 4. HE-SIG-B HE SIGNAL B
N.sub.HESIGB * 3.2 .mu.s 0.8 .mu.s 312.5 kHz N.sub.HESIGB means the
number of field 4 .mu.s OFDM symbols of the HE-SIG-B field and is
variable. DL MU packet contains HE-SIG-B. SU packets and UL Trigger
based packets do not contain HE-SIG-B. HE-STF HE Short 4 or 8 .mu.s
-- -- non- HE-STF of a non-trigger-based Training field trigger-
PPDU has a periodicity of 0.8 .mu.s based with 5 periods. A
non-trigger-based PPDU: PPDU is not sent in response to a
(equivalent trigger frame. to) 1,250 The HE-STF of a trigger-based
kHz; PPDU has a periodicity of 1.6 .mu.s trigger- with 5 periods. A
trigger-based based PPDU is an UL PPDU sent in PPDU: response to a
trigger frame. (equivalent to) 625 kHz HE-LTF HE Long N.sub.HELTF *
2xLTF: supports 2xLTF: HE PPDU shall support 2xLTF Training field
(DTF 6.4 .mu.s 0.8, 1.6, (equivalent mode and 4xLTF mode. period +
4xLTF: 3.2 .mu.s to) 156.25 In the 2xLTF mode, HE-LTF GI) .mu.s
12.8 .mu.s kHz; symbol excluding GI is equivalent 4xLTF: to
modulating every other tone in 78.125 kHz an OFDM symbol of 12.8
.mu.s excluding GI, and then removing the second half of the OFDM
symbol in time domain. N.sub.HELTF means the number of HE- LTF
symbols and is equal to 1, 2, 4, 6, 8. HE-DATA HE DATA N.sub.DATA *
12.8 .mu.s supports 78.125 kHz N.sub.DATA means the number of HE
field (DTF 0.8, 1.6, data symbols. period + 3.2 .mu.s GI) .mu.s
[0103] L-STF is a non-HT Short Training field and may have a
duration of 8 .mu.s and a subcarrier spacing equivalent to 1250
kHz. L-STF of a PPDU which is not based on a trigger may have a
periodicity of 0.8 .mu.s with 10 periods. Herein, the trigger
corresponds to scheduling information for UL transmission.
[0104] L-LTF is a non-HT Long Training field and may have a
duration of 8 .mu.s, a DFT period of 3.2 .mu.s, a Guard Interval
(GI) of 1.6 .mu.s, and a subcarrier spacing of 312.5 kHz.
[0105] L-SIG is a non-HT SIGNAL field and may have a duration of 4
.mu.s, a DFT period of 3.2 .mu.s, a GI of 0.8 .mu.s, and a
subcarrier spacing of 312.5 kHz.
[0106] RL-SIG is a Repeated Non-HT SIGNAL field and may have a
duration of 4 .mu.s, a DFT period of 3.2 .mu.s, a GI of 0.8 .mu.s,
and a subcarrier spacing of 312.5 kHz.
[0107] L-STF, L-LTF, L-SIG, and RL-SIG may be called legacy
preambles.
[0108] HE-SIG-A is a HE SIGNAL A field and may have a duration of
N.sub.HESIGA*4 .mu.s, a DFT period of 3.2 .mu.s, a GI of 0.8 .mu.s,
and a subcarrier spacing of 312.5 kHz. HE-SIG-A may be duplicated
on each 20 MHz segment after the legacy preambles to indicate
common control information. N.sub.HESIGA represents the number of
OFDM symbols of the HE-SIG-A field and may have a value of 2 or
4.
[0109] HE-SIG-B is a HE SIGNAL B field and may have a duration of
N.sub.HESIGB*4 .mu.s, a DFT period of 3.2 .mu.s, a GI of 0.8 .mu.s,
and a subcarrier spacing of 312.5 kHz. N.sub.HESIGB represents the
number of OFDM symbols of the HE-SIG-B field and may have a
variable value. In addition, although a DL Multi-User (MU) packet
may include the HE-SIG-B field, a Single-User (SU) packet and a UL
trigger based packet may not include the HE-SIG-B field.
[0110] HE-STF is a HE Short Training field and may have a duration
of 4 or 8 .mu.s. A non-trigger based PPDU may have a subcarrier
spacing equivalent to 1250 kHz and a trigger based PPDU may have a
subcarrier spacing equivalent to 625 kHz. HE-STF of the
non-triggered PPDU may have a periodicity of 0.8 .mu.s with 4
periods. The non-triggered PPDU is not transmitted in response to a
trigger field. HE-STF of the trigger based PPDU may have a
periodicity of 1.6 .mu.s with 5 periods. The trigger based PPDU is
a UL PPDU transmitted in response to the trigger frame.
[0111] HE-LTF is a HE Long Training field and may have a duration
of N.sub.HELTF*(DFT period+GI).mu.s. N.sub.HELTF represents the
number of HE-LTF symbols and may have a value of 1, 2, 4, 6, or 8.
A HE PPDU may support a 2.times.LTF mode and a 4.times.LTF mode. In
the 2.times.LTF mode, a HE-LTF symbol except for a GI is equivalent
to a symbol obtained by modulating every other tone in an OFDM
symbol of 12.8 .mu.s excluding a GI and then eliminating the first
half or the second half of the OFDM symbol in the time domain. In
the 4.times.LTF mode, a HE-LTF symbol excluding a GI are equivalent
to a symbol obtained by modulating every fourth tone in an OFDM
symbol of 12.8 .mu.s excluding a GI and then eliminating the first
three-fourths or the last three-fourths of the OFDM symbol in the
time domain. 2.times.LTF may have a DFT period of 6.4 .mu.s and
4.times.LTF may have a DFT period of 12.8 .mu.s. A GI of HE-LTF may
support 0.8 .mu.s, 1.6 .mu.s, and 3.2 .mu.s. 2.times.LTF may have a
subcarrier spacing equivalent to 156.25 kHz and 4.times.LTF may
have a subcarrier spacing of 78.125 kHz.
[0112] HE-DATA is a HE DATA field and may have a duration of,
N.sub.DATA*(DFT period+GI).mu.s. N.sub.DATA represents the number
of HE-DATA symbols. HE-DATA may have a DFT period of 12.8 .mu.s. A
GI of HE-DATA may support 0.8 .mu.s, 1.6 .mu.s, and 3.2 .mu.s.
HE-DATA may have a subcarrier spacing of 78.125 kHz.
[0113] The above description of the fields included in the HE PPDU
frame format may be combined with exemplary HE PPDU frame formats
described below. For example, characteristics of fields exemplarily
described below may be applied while a transmission order of the
fields of the HE PPDU frame format of FIG. 7 is maintained.
[0114] FIG. 8 depicts an exemplary HE PPDU frame format according
to the present disclosure.
[0115] Referring to FIG. 8, the vertical axis represents frequency
and the horizontal axis represents time. It is assumed that
frequency and time increase in the upward direction and the right
direction, respectively.
[0116] In the example of FIG. 8, one channel includes four
subchannels. An L-STF, an L-LTF, an L-SIG, and an HE-SIG-A may be
transmitted per channel (e.g., 20 MHz), a HE-STF and a HE-LTF may
be transmitted on each subchannel being a basic subchannel unit
(e.g., 5 MHz), and a HE-SIG-B and a PSDU may be transmitted on each
of subchannels allocated to a STA. A subchannel allocated to a STA
may have a size required for PSDU transmission to the STA. The size
of the subchannel allocated to the STA may be N (N=1, 2, 3, . . . )
times as large as the size of basic subchannel unit (i.e., a
subchannel having a minimum size). In the example of FIG. 8, the
size of a subchannel allocated to each STA is equal to the size of
the basic subchannel unit. For example, a first subchannel may be
allocated for PSDU transmission from an AP to STA1 and STA2, a
second subchannel may be allocated for PSDU transmission from the
AP to STA3 and STA4, a third subchannel may be allocated for PSDU
transmission from the AP to STA5, and a fourth subchannel may be
allocated for PSDU transmission from the AP to STA6.
[0117] While the term subchannel is used in the present disclosure,
the term subchannel may be referred to as Resource Unit (RU) or
subband. In particular, the terms like OFDMA subchannel, OFDMA RU,
OFDMA subband can be used in embodiments for OFDMA in the present
disclosure. Terms like a bandwidth of a subchannel, a number of
tones (or subcarriers) allocated to a subchannel, a number of data
tones (or data subcarriers) allocated to a subchannel can be used
to express a size of a subchannel. A subchannel refers to a
frequency band allocated to a STA and a basic subchannel unit
refers to a basic unit used to represent the size of a subchannel.
While the size of the basic subchannel unit is 5 MHz in the above
example, this is purely exemplary. Thus, the basic subchannel unit
may have a size of 2.5 MHz.
[0118] In FIG. 8, a plurality of HE-LTF elements are distinguished
in the time and frequency domains. One HE-LTF element may
correspond to one OFDM symbol in time domain and one subchannel
unit (i.e., a subchannel bandwidth allocated to a STA) in frequency
domain. The HE-LTF elements are logical units, and the PHY layer
does not necessarily operate in units of an HE-LTF element. In the
following description, a HE-LTF element may be referred to shortly
as a HE-LTF.
[0119] A HE-LTF symbol may correspond to a set of HE-LTF elements
in one OFDM symbol in time domain and in one channel unit (e.g., 20
MHz) in frequency domain.
[0120] A HE-LTF section may correspond to a set of HE-LTF elements
in one or more OFDM symbols in time domain and in one subchannel
unit (i.e., a subchannel bandwidth allocated to a STA) in frequency
domain.
[0121] A HE-LTF field may be a set of HE-LTF elements, HE-LTF
symbols, or HE-LTF sections for a plurality of stations.
[0122] The L-STF field is used for frequency offset estimation and
phase offset estimation, for preamble decoding at a legacy STA
(i.e., a STA operating in a system such as IEEE 802.11a/b/g/n/ac).
The L-LTF field is used for channel estimation, for the preamble
decoding at the legacy STA. The L-SIG field is used for the
preamble decoding at the legacy STA and provides a protection
function for PPDU transmission of a third-party STA (e.g., setting
a NAV based on the value of a LENGTH field included in the L-SIG
field).
[0123] HE-SIG-A (or HEW SIG-A) represents High Efficiency Signal A
(or High Efficiency WLAN Signal A), and includes HE PPDU (or HEW
PPDU) modulation parameters, etc. for HE preamble (or HEW preamble)
decoding at a HE STA (or HEW STA). The parameters set included in
the HEW SIG-A field may include one or more of Very High Throughput
(VHT) PPDU modulation parameters transmitted by IEEE 802.11ac
stations, as listed in [Table 2] below, to ensure backward
compatibility with legacy STAs (e.g., IEEE 802.11ac stations).
TABLE-US-00002 TABLE 2 Two parts of Number VHT-SIG-A Bit Field of
bits Description VHT-SIG-A1 B0-B1 BW 2 Set to 0 for 20 MHz, 1 for
40 MHz, 2 for 80 MHz, and 3 for 160 MHz and 80 + 80 MHz B2 Reserved
1 Reserved. Set to 1. B3 STBC 1 For a VHT SU PPDU: Set to 1 if
space time block coding is used and set to 0 otherwise. For a VHT
MU PPDU: Set to 0. B4-B9 Group ID 6 Set to the value of the
TXVECTOR parameter GROUP_ID. A value of 0 or 63 indicates a VHT SU
PPDU; otherwise, indicates a VHT MU PPDU. B10-B21 NSTS/Partial 12
For a VHT MU PPDU: NSTS is divided into 4 user AID positions of 3
bits each. User position p, where 0 .ltoreq. p .ltoreq. 3, uses
bits B(10 + 3p) to B(12 + 3p). The number of space- time streams
for user u are indicated at user position p = USER_POSITION[u]
where u = 0, 1, . . . , NUM_USERS - 1 and the notation A[b] denotes
the value of array A at index b. Zero space-time streams are
indicated at positions not listed in the USER_POSITION array. Each
user position is set as follows: Set to 0 for 0 space-time streams
Set to 1 for 1 space-time stream Set to 2 for 2 space-time streams
Set to 3 for 3 space-time streams Set to 4 for 4 space-time streams
Values 5-7 are reserved For a VHT SU PPDU: B10-B12 Set to 0 for 1
space-time stream Set to 1 for 2 space-time streams Set to 2 for 3
space-time streams Set to 3 for 4 space-time streams Set to 4 for 5
space-time streams Set to 5 for 6 space-time streams Set to 6 for 7
space-time streams Set to 7 for 8 space-time streams B13-B21
Partial AID: Set to the value of the TXVECTOR parameter
PARTIAL_AID. Partial AID provides an abbreviated indication of the
intended recipient(s) of the PSDU (see 9.17a). B22
TXOP_PS_NOT_ALLOWED 1 Set to 0 by VHT AP if it allows non-AP VHT
STAs in TXOP power save mode to enter Doze state during a TXOP. Set
to 1 otherwise. The bit is reserved and set to 1 in VHT PPDUs
transmitted by a non-AP VHT STA. B23 Reserved 1 Set to 1 VHT-SIG-A2
B0 Short G1 1 Set to 0 if short guard interval is not used in the
Data field. Set to 1 if short guard interval is used in the Data
field. B1 Short G1 1 Set to 1 if short guard interval is used and
N.sub.SYM mod 10 = 9; N.sub.SYM otherwise, set to 0. N.sub.SYM is
defined in 22.4.3. Disambiguation B2 SU/MU[0] 1 For a VHT SU PPDU,
B2 is set to 0 for BCC, 1 for LDPC Coding For a VHT MU PPDU, if the
MU[0] NSTS field is nonzero, then B2 indicates the coding used for
user u with USER_POSITION[u] = 0; set to 0 for BCC and 1 for LDPC.
If the MU[0] NSTS field is 0, then this field is reserved and set
to 1. B3 LDPC Extra 1 Ser to 1 if the LDPC PPDU encoding process
(if an SU OFDM PPDU), or at least one LDPC user's PPDU encoding
process Symbol (if a VHT MU PPDU), results in an extra OFDM symbol
(or symbols) as described in 22.3.10.5.4 and 22.3.10.5.5. Set to 0
otherwise. B4-B7 SU VHT- 4 For a VHT SU PPDU: MCS/MU[1-3] VHT-MCS
index Coding For a VHT MU PPDU: If the MU[1] NSTS field is nonzero,
then B4 indicates coding for user u with USER_POSITION[u] = 1: set
to 0 for BCC, 1 for LDPC. If the MU[1] NSTS field is 0, then B4 is
reserved and set to 1. If the MU[2] NSTS field is nonzero, then B5
indicates coding for user u with USER_POSITION[u] = 2: set to 0 for
BCC, 1 for LDPC. If the MU[2] NSTS field is 0, then B5 is reserved
and set to 1. If the MU[3] NSTS field is nonzero, then B6 indicates
coding for user u with USER_POSITION[u] = 3: set to 0 for BCC, 1
for LDPC. If the MU[3] NSTS field is 0, then B6 is reserved and set
to 1. B7 is reserved and set to 1 B8 Beamformed 1 For a VHT SU
PPDU: Set to 1 if a Beamforming steering matrix is applied to the
waveform in an SU transmission as described in 20.3.11.11.2. set to
0 otherwise. For a VHT MU PPDU: Reserved and set to 1 NOTE-If equal
to 1 smoothing is not recommended. B9 Reserved 1 Reserved and set
to 1 B10-B17 CRC 8 CRC calculated as in 20.3.9.4.4 with c7 in B10.
Bits 0-23 of HT-SIG1 and bits 0-9 of HT-SIG2 are replaced by bits
0.23 of VHT-SIG-A1 and bits 0-9 of VHT-SIG-A2, respectively.
B18-B23 Tail 6 Used to terminate the trellis of the convolutional
decoder. Set to 0.
[0124] [Table 2] illustrates fields, bit positions, numbers of
bits, and descriptions included in each of two parts, VHT-SIG-A1
and VHT-SIG-A2, of the VHT-SIG-A field defined by the IEEE 802.11ac
standard. For example, a BW (BandWidth) field occupies two Least
Significant Bits (LSBs), B0 and B1 of the VHT-SIG-A1 field and has
a size of 2 bits. If the 2 bits are set to 0, 1, 2, or 3, the BW
field indicates 20 MHz, 40 MHz, 80 MHz, or 160 and 80+80 MHz. For
details of the fields included in the VHT-SIG-A field, refer to the
IEEE 802.11ac-2013 technical specification. In the HE PPDU frame
format of the present disclosure, the HE-SIG-A field may include
one or more of the fields included in the VHT-SIG-A field, and it
may provide backward compatibility with IEEE 802.11ac stations.
[0125] FIG. 9 depicts subchannel allocation in the HE PPDU frame
format according to the present disclosure.
[0126] In FIG. 9, it is assumed that information indicating
subchannels allocated to STAs in HE PPDU indicates that 0 MHz
subchannel is allocated to STA1 (i.e., no subchannel is allocated),
a 5-MHz subchannel is allocated to each of STA2 and STA3, and a
10-MHz subchannel is allocated to STA4.
[0127] In the example of FIG. 9, an L-STF, an L-LTF, an L-SIG, and
a HE-SIG-A may be transmitted per channel (e.g., 20 MHz), a HE-STF
and a HE-LTF may be transmitted on each of subchannels being basic
subchannel units (e.g., 5 MHz), and a HE-SIG-B and a PSDU may be
transmitted on each of subchannels allocated to STAs. A subchannel
allocated to a STA has a size required for PSDU transmission to the
STA. The size of the subchannel allocated to the STA may be an N
(N=1, 2, 3, . . . ) multiple of the size of the basic subchannel
unit (i.e., a minimum-size subchannel unit). In the example of FIG.
9, the size of a subchannel allocated to STA2 is equal to that of
the basic subchannel unit, the size of a subchannel allocated to
STA3 is equal to that of the basic subchannel unit, and the size of
a subchannel allocated to STA4 is twice larger than that of the
basic subchannel unit.
[0128] FIG. 9 illustrates a plurality of HE-LTF elements and a
plurality of HE-LTF subelements which are distinguished in the time
and frequency domains. One HE-LTF element may correspond to one
OFDM symbol in the time domain and one subchannel unit (i.e., the
bandwidth of a subchannel allocated to a STA) in the frequency
domain. One HE-LTF subelement may correspond to one OFDM symbol in
the time domain and one basic subchannel unit (e.g. 5 MHz) in the
frequency domain. In the example of FIG. 9, one HE-LTF element
includes one HE-LTF subelement in the 5-MHz subchannel allocated to
STA2 or STA3. On the other hand, one HE-LTF element includes two
HE-LTF subelements in the third subchannel, i.e., 10-MHz
subchannel, allocated to STA4. A HE-LTF element and a HE-LTF
subelement are logical units and the PHY layer does not always
operate in units of a HE-LTF element or HE-LTF subelement.
[0129] A HE-LTF symbol may correspond to a set of HE-LTF elements
in one OFDM symbol in the time domain and one channel unit (e.g. 20
MHz) in the frequency domain. That is, one HE-LTF symbol may be
divided into HE-LTF elements by a subchannel width allocated to a
STA and into HE-LTF subelements by the width of the basic
subchannel unit in the frequency domain.
[0130] A HE-LTF section may correspond to a set of HE-LTF elements
in one or more OFDM symbols in the time domain and one subchannel
unit (i.e. the bandwidth of a subchannel allocated to a STA) in the
frequency domain. A HE-LTF subsection may correspond to a set of
HE-LTF elements in one or more OFDM symbols in the time domain and
one basic subchannel unit (e.g., 5 MHz) in the frequency domain. In
the example of FIG. 9, one HE-LTF section includes one HE-LTF
subsection in the 5-MHz subchannel allocated to STA2 or STA3. On
the other hand, one HE-LTF section includes two HE-LTF subsections
in the third subchannel, i.e., 10-MHz subchannel, allocated to
STA4.
[0131] A HE-LTF field may correspond to a set of HE-LTF elements
(or subelements), HE-LTF symbols, or HE-LTF sections (or
subsections) for a plurality of stations.
[0132] For the afore-described HE PPDU transmission, subchannels
allocated to a plurality of HE STAs may be contiguous in the
frequency domain. In other words, for HE PPDU transmission, the
subchannels allocated to the HE STAs may be sequential and any
intermediate one of the subchannels of one channel (e.g., 20 MHz)
may not be allowed to be unallocated or empty. Referring to FIG. 8,
if one channel includes four subchannels, it may not be allowed to
keep the third subchannel unallocated and empty, while the first,
second, and fourth subchannels are allocated to STAs. However, the
present disclosure does not exclude non-allocation of an
intermediate subchannel of one channel to a STA.
[0133] FIG. 10 depicts a subchannel allocation method according to
the present disclosure.
[0134] In the example of FIG. 10, a plurality of contiguous
channels (e.g., 20-MHz-bandwidth channels) and boundaries of the
plurality of contiguous channels are shown. In FIG. 10, a preamble
may correspond to an L-STF, an L-LTF, an L-SIG, and a HE-SIG-A as
illustrated in the examples of FIGS. 8 and 9.
[0135] A subchannel for each HE STA may be allocated only within
one channel, and may not be allocated with partially overlapping
between a plurality of channels. That is, if there are two
contiguous 20-MHz channels CH1 and CH2, subchannels for STAs paired
for MU-MIMO-mode or OFDMA-mode transmission may be allocated either
within CH1 or within CH2, and it may be prohibited that one part of
a subchannel exists in CH1 and another part of the subchannel
exists in CH2. This means that one subchannel may not be allocated
with crossing a channel boundary. From the perspective of RUs
supporting the MU-MIMO or OFDMA mode, a bandwidth of 20 MHz may be
divided into one or more RUs, and a bandwidth of 40 MHz may be
divided into one or more RUs in each of two contiguous 20-MHz
bandwidths, and no RU is allocated with crossing the boundary
between two contiguous 20-MHz bandwidths.
[0136] As described above, it is not allowed that one subchannel
belongs to two or more 20-MHz channels. Particularly, a 2.4-GHz
OFDMA mode may support a 20-MHz OFDMA mode and a 40-MHz OFDMA mode.
In the 2.4-GHz OFDMA mode, it may not be allowed that one
subchannel belongs to two or more 20-MHz channels.
[0137] FIG. 10 is based on the assumption that subchannels each
having the size of a basic subchannel unit (e.g., 5 MHz) in CH1 and
CH2 are allocated to STA1 to STA7, and subchannels each having
double the size (e.g., 10 MHz) of the basic subchannel unit in CH4
and CH5 are allocated to STA8, STA9, and STA10.
[0138] As illustrated in the lower part of FIG. 9, although a
subchannel allocated to STA1, STA2, STA3, STA5, STA6, or STA7 is
fully overlapped only with one channel (i.e., without crossing the
channel boundary, or belonging only to one channel), a subchannel
allocated to STA4 is partially overlapped with the two channels
(i.e., crossing the channel boundary, or belonging to the two
channels). In the forgoing example of the present disclosure, the
subchannel allocation to STA4 is not allowed.
[0139] As illustrated in the upper part of FIG. 9, although a
subchannel allocated to STA8 or STA10 is fully overlapped only with
one channel (i.e., crossing the channel boundary, or belonging only
to one channel), a subchannel allocated to STA9 is partially
overlapped with two channels (i.e., crossing the channel boundary,
or belonging to the two channels). In the forgoing example of the
present disclosure, the subchannel allocation to STA9 is not
allowed.
[0140] On the other hand, it may be allowed to allocate a
subchannel partially overlapped between a plurality of channels
(i.e., crossing the channel boundary, or belonging to two
channels). For example, in SU-MIMO mode transmission, a plurality
of contiguous channels may be allocated to a STA and any of one or
more subchannels allocated to the STA may cross the boundary
between two contiguous channels.
[0141] While the following description is given with an assumption
that one subchannel has a channel bandwidth of 5 MHz in one channel
having a channel bandwidth of 20 MHz, this is provided to simplify
the description of the principle of the present disclosure and thus
should not be construed as limiting the present disclosure. For
example, the bandwidths of a channel and a subchannel may be
defined or allocated as values other than the above examples. In
addition, a plurality of subchannels in one channel may have the
same or different channel widths.
[0142] FIG. 11 depicts the starting and ending points of a HE-LTF
field in the HE PPDU frame format according to the present
disclosure.
[0143] To support the MU-MIMO mode and the OFDMA mode, the HE PPDU
frame format according to the present disclosure may include, in
the HE-SIG-A field, information about the number of spatial streams
to be transmitted to a HE STA allocated to each subchannel.
[0144] If MU-MIMO-mode or OFDMA-mode transmission is performed to a
plurality of HE STAs on one subchannel, the number of spatial
streams to be transmitted to each of the HE STAs may be provided in
the HE-SIG-A or HE-SIG-B field, which will be described later in
detail.
[0145] FIG. 11 is based on the assumption that a first 5-MHz
subchannel is allocated to STA1 and STA2 and two spatial streams
are transmitted to each STA in a DL MU-MIMO or OFDMA mode (i.e., a
total of four spatial streams are transmitted on one subchannel).
For this purpose, a HE-STF, a HE-LTF, a HE-LTF, a HE-LTF, a HE-LTF,
and a HE-SIG-B follow the HE-SIG-A field on the subchannel. The
HE-STF is used for frequency offset estimation and phase offset
estimation for the 5-MHz subchannel. The HE-LTFs are used for
channel estimation for the 5-MHz subchannel. Since the subchannel
carries four spatial streams, as many HE-LTFs (i.e., HE-LTF symbols
or HE-LTF elements in a HE-LTF section) as the number of the
spatial streams, that is, four HE-LTFs are required to support
MU-MIMO transmission.
[0146] According to an example of the present disclosure,
relationship between a total number of spatial streams transmitted
on one subchannel and a number of HE-LTFs is listed in [Table
3].
TABLE-US-00003 TABLE 3 Total number of spatial streams transmitted
on one subchannel Number of HE-LTFs 1 1 2 2 3 4 4 4 5 6 6 6 7 8 8
8
[0147] Referring to [Table 3], if one spatial stream is transmitted
on one subchannel, at least one HE-LTF needs to be transmitted on
the subchannel. If an even number of spatial streams are
transmitted on one subchannel, at least as many HE-LTFs as the
number of the spatial streams need to be transmitted. If an odd
number of spatial streams greater than one are transmitted on one
subchannel, at least as many HE-LTFs as a number of adding 1 to the
number of the spatial streams need to be transmitted.
[0148] Referring to FIG. 11 again, it is assumed that the second
5-MHz subchannel is allocated to STA3 and STA4 and one spatial
streams per STA is transmitted in the DL MU-MIMO or OFDMA mode
(i.e., a total of two spatial streams are transmitted on one
subchannel). In this case, two HE-LTFs need to be transmitted on
the second subchannel, however, in the example of FIG. 11, a
HE-STF, a HE-LTF, a HE-LTF, a HE-LTF, a HE-LTF, and a HE-SIG-B
follow the HE-SIG-A field on the subchannel (i.e., four HE-LTFs are
transmitted). This is for setting the same starting time of PSDU
transmission for subchannels allocated to other STAs paired with
STA3 and STA4 for MU-MIMO transmission. If only two HE-LTFs are
transmitted on the second subchannel, PSDUs are transmitted at
different time points on the first and second subchannels. PSDU
transmission on each subchannel at a different time point results
in discrepancy between OFDM symbol timings of subchannels, thereby
no orthogonality is maintained. To overcome this problem, an
additional constraint need to be imposed for HE-LTF
transmission.
[0149] Basically, transmission of as many HE-LTFs as required is
sufficient in an SU-MIMO or non-OFDMA mode. However, timing
synchronization (or alignment) with fields transmitted on
subchannels for other paired STAs is required in the MU-MIMO or
OFDMA mode. Accordingly, the numbers of HE-LTFs may be determined
for all other subchannels based on a subchannel having the maximum
number of streams in MU-MIMO-mode or OFDMA-mode transmission.
[0150] Specifically, the numbers of HE-LTFs may be determined for
all subchannels according to the maximum of the numbers of HE-LTFs
(HE-LTF symbols or HE-LTF elements in a HE-LTF section) required
according to the total numbers of spatial streams transmitted on
each subchannel, for a set of HE STAs allocated to each subchannel.
A "set of HE STAs allocated to each subchannel" is one HE STA in
the SU-MIMO mode, and a set of HE STAs paired across a plurality of
subchannels in the MU-MIMO mode. The `number of spatial streams
transmitted on each subchannel` is the number of spatial streams
transmitted to one HE STA in the SU-MIMO mode, and the number of
spatial streams transmitted to a plurality of HE STAs paired on the
subchannel in the MU-MIMO mode.
[0151] That is, it may be said that a HE-LTF field starts at the
same time point and ends at the same time point in a HE PPDU for
all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-mode
transmission. Or it may be said that the lengths of HE-LTF sections
are equal on a plurality of subchannels for all users (i.e. HE
STAs) in MU-MIMO-mode or OFDMA-mode transmission. Or it may be said
that the number of HE-LTF elements included in each HE-LTF section
is equal on a plurality of subchannels for all users (i.e. HE STAs)
in MU-MIMO-mode or OFDMA-mode transmission. Accordingly, PSDU
transmission timings may be synchronized among a plurality of
subchannels for all HE STAs in MU-MIMO-mode or OFDMA-mode
transmission.
[0152] As described above, the number of HE-LTF symbols (refer to
FIG. 8) may be 1, 2, 4, 6, or 8 in HE PPDU transmission in the
MU-MIMO or OFDMA mode, determined according to the maximum of the
numbers of spatial streams on each of a plurality of subchannels. A
different number of spatial streams may be allocated to each of a
plurality of subchannels, and the number of spatial streams
allocated to one subchannel is the number of total spatial streams
for all users allocated to the subchannel. That is, the number of
HE-LTF symbols may be determined according to the number of spatial
streams allocated to a subchannel having a maximum number of
spatial streams by comparing the number of total spatial streams
for all users allocated to one of a plurality of subchannels with
the number of total spatial streams for all users allocated to
another subchannel.
[0153] Specifically, in HE PPDU transmission in the OFDMA mode, the
number of HE-LTF symbols may be 1, 2, 4, 6, or 8, determined based
on the number of spatial streams transmitted in a subchannel having
a maximum number of spatial streams across a plurality of
subchannels. Further, in HE PPDU transmission in the OFDMA mode,
the number of HE-LTF symbols may be determined based on whether the
number of spatial streams transmitted in a subchannel having a
maximum number of spatial streams across a plurality of subchannels
is odd or even (refer to [Table 3]). That is, in HE PPDU
transmission in the OFDMA mode, when the number (e.g., K) of
spatial streams transmitted in a subchannel having a maximum number
of spatial streams across a plurality of subchannels is an even
number, the number of HE-LTF symbols may be equal to K. In HE PPDU
transmission in the OFDMA mode, when the number, K, of spatial
streams transmitted in a subchannel having a maximum number of
spatial streams across a plurality of subchannels is an odd number
greater than one, the number of HE-LTF symbols may be equal to
K+1.
[0154] When only one STA is allocated to one subchannel in OFDMA
mode (i.e., OFDMA mode without using MU-MIMO), a subchannel having
a maximum number of spatial streams across a plurality of
subchannels may be determined by the number of spatial streams for
a STA allocated to each subchannel. When more than one STA is
allocated to one subchannel in OFDMA mode (i.e., OFDMA mode using
MU-MIMO), a subchannel having a maximum number of spatial streams
across a plurality of subchannels may be determined by the number
of STAs allocated to each subchannel and the number of spatial
streams for each STA allocated to each subchannel (e.g., if STA1
and STA2 are allocated to one subchannel, sum of the number of
spatial streams for STA1 and the number of spatial streams for
STA2).
[0155] When transmitting a HE PPDU frame in the MU-MIMO or OFDMA
mode, a transmitter may generate P (P is an integer equal to or
larger than 1) HE-LTF symbols (refer to FIG. 8) and transmit a HE
PPDU frame including at least the P HE-LTF symbols and a Data field
to a receiver. The HE PPDU frame may be divided into Q subchannels
in the frequency domain (Q is an integer equal to or larger than
2). Each of the P HE-LTF symbols may be divided into Q HE-LTF
elements corresponding to the Q subchannels in the frequency
domain. That is, the HE PPDU may include P HE-LTF elements on one
subchannel (herein, the P HE-LTF elements may belong to one HE-LTF
section on the subchannel).
[0156] As described above, the number of HE-LTF elements (i.e., P)
in one of the Q subchannels may be equal to the number of HE-LTF
elements (i.e. P) of another subchannel. Also, the number of HE-LTF
elements (i.e., P) included in a HE-LTF section in one of the Q
subchannels may be equal to the number of HE-LTF elements (i.e. P)
included in a HE-LTF section in another subchannel. The HE-LTF
section of one of the Q subchannels may start and end at the same
time points as the HE-LTF section of another subchannel. Also, the
HE-LTF sections may start and end at the same time points across
the Q subchannels (i.e., across all users or stations).
[0157] Referring to FIG. 11 again, the third 5-MHz subchannel is
allocated to STA5 and one spatial stream is transmitted on the
subchannel in SU-MIMO (considering all subchannels, a plurality of
spatial streams are transmitted to STA1 to STA6 in MU-MIMO or OFDMA
mode). In this case, although transmission of one HE-LTF is
sufficient for the subchannel, as many HE-LTFs as the maximum of
the numbers of HE-LTFs on the other subchannels, that is, four
HE-LTFs are transmitted on the subchannel in order to align the
starting points and ending points of the HE-LTF fields of the
subchannels.
[0158] The fourth 5-MHz subchannel is allocated to STA6 and one
spatial stream is transmitted on the subchannel in SU-MIMO
(considering all other subchannels, a plurality of spatial streams
are transmitted to STA1 to STA6 in MU-MIMO or OFDMA mode). In this
case, although transmission of one HE-LTF is sufficient for the
subchannel, as many HE-LTFs as the maximum of the numbers of
HE-LTFs on the other subchannels, that is, four HE-LTFs are
transmitted on the subchannel in order to align the starting points
and ending points of the HE-LTF fields of the subchannels.
[0159] In the example of FIG. 11, the remaining two HE-LTFs except
two HE-LTFs required for channel estimation of STA3 and STA4 on the
second subchannel, the remaining three HE-LTFs except one HE-LTF
required for channel estimation of STA5 on the third subchannel,
and the remaining three HE-LTFs except one HE-LTF required for
channel estimation of STA6 on the fourth subchannel may be said to
be placeholders that are actually not used for channel estimation
at the STAs.
[0160] FIG. 12 depicts a HE-SIG-B field and a HE-SIG-C field in the
HE PPDU frame format according to the present disclosure.
[0161] To effectively support MU-MIMO-mode or OFDMA-mode
transmission in the HE PPDU frame format according to the present
disclosure, independent signaling information may be transmitted on
each subchannel. Specifically, a different number of spatial
streams may be transmitted to each of a plurality of HE STAs that
receive an MU-MIMO-mode or OFDMA-mode transmission simultaneously.
Therefore, information about the number of spatial streams to be
transmitted should be indicated to each HE STA.
[0162] Information about the number of spatial streams on one
channel may be included in, for example, a HE-SIG-A field. A
HE-SIG-B field may include spatial stream allocation information
about one subchannel. Also, a HE-SIG-C field may be transmitted
after transmission of HE-LTFs, including Modulation and Coding
Scheme (MCS) information about a PSDU and information about the
length of the PSDU, etc.
[0163] With reference to the foregoing examples of the present
disclosure, mainly the features of a HE PPDU frame structure
applicable to a DL MU-MIMO-mode or OFDMA-mode transmission that an
AP transmits simultaneously to a plurality of STAs have been
described. Now, a description will be given of the features of a HE
PPDU frame structure applicable to a UL MU-MIMO-mode or OFDMA-mode
transmission that a plurality of STAs transmits simultaneously to
an AP.
[0164] The above-described various examples of structures of the HE
PPDU frame format supporting MU-MIMO-mode or OFDMA-mode
transmission should not be understood as applicable only to DL
without applicable UL. Rather, the examples should be understood as
also applicable to UL. For example, the above-described exemplary
HE PPDU frame formats may also be used for a UL HE PPDU
transmission that a plurality of STAs simultaneously transmits to a
single AP.
[0165] However, in the case of a DL MU-MIMO-mode or OFDMA-mode HE
PPDU transmission that an AP simultaneously transmits to a
plurality of STAs, the transmission entity, AP has knowledge of the
number of spatial streams transmitted to a HE STA allocated to each
of a plurality of subchannels. Therefore, the AP may include, in a
HE-SIG-A field or a HE-SIG-B field, information about the total
number of spatial streams transmitted across a channel, a maximum
number of spatial streams (i.e., information being a basis of the
number of HE-LTF elements (or the starting point and ending point
of a HE-LTF section) on each subchannel), and the number of spatial
streams transmitted on each subchannel. In contrast, in the case of
a UL MU-MIMO-mode or OFDMA-mode HE PPDU transmission that a
plurality of STAs simultaneously transmits to an AP, each STA being
a transmission entity may be aware only of the number of spatial
streams in a HE PSDU that it will transmit, without knowledge of
the number of spatial streams in a HE PSDU transmitted by another
STA paired with the STA. Accordingly, the STA may determine neither
the total number of spatial streams transmitted across a channel
nor a maximum number of spatial streams.
[0166] To solve this problem, a common parameter (i.e., a parameter
applied commonly to STAs) and an individual parameter (a separate
parameter applied to an individual STA) may be configured as
follows in relation to a UL HE PPDU transmission.
[0167] For simultaneous UL HE PPDU transmissions from a plurality
of STAs to an AP, a protocol may be designed in such a manner that
the AP sets a common parameter or individual parameters
(common/individual parameters) for the STAs for the UL HE PPDU
transmissions and each STA operates according to the
common/individual parameters. For example, the AP may transmit a
trigger frame (or polling frame) for a UL MU-MIMO-mode or
OFDMA-mode transmission to a plurality of STAs. The trigger frame
may include a common parameter (e.g., the number of spatial streams
across a channel or a maximum number of spatial streams) and
individual parameters (e.g., the number of spatial streams
allocated to each subchannel), for the UL MU-MIMO-mode or
OFDMA-mode transmission. As a consequence, a HE PPDU frame format
applicable to a UL MU-MIMO or OFDMA mode may be configured without
a modification to an exemplary HE PPDU frame format applied to a DL
MU-MIMO or OFDMA mode. For example, each STA may configure a HE
PPDU frame format by including information about the number of
spatial streams across a channel in a HE-SIG-A field, determining
the number of HE-LTF elements (or the starting point and ending
point of a HE-LTE section) on each subchannel according to the
maximum number of spatial streams, and including information about
the number of spatial streams for the individual STA in a HE-SIG-B
field.
[0168] Alternatively, if the STAs operate always according to the
common/individual parameters received in the trigger frame from the
AP, each STA does not need to indicate the common/individual
parameters to the AP during a HE PPDU transmission. Therefore, this
information may not be included in a HE PPDU. For example, each STA
may have only to determine the total number of spatial streams, the
maximum number of spatial streams, and the number of spatial
streams allocated to individual STA, as indicated by the AP, and
configure a HE PPDU according to the determined numbers, without
including information about the total number of spatial streams or
the number of spatial streams allocated to the STA in the HE
PPDU.
[0169] On the other hand, if the AP does not provide
common/individual parameters in a trigger frame, for a UL MIMO-mode
or OFDMA-mode HE PPDU transmission, the following operation may be
performed.
[0170] Common transmission parameters (e.g., channel BandWidth (BW)
information, etc.) for simultaneously transmitted HE PSDUs may be
included in HE-SIG-A field, but parameters that may be different
for individual STAs (e.g., the number of spatial streams, an MCS,
and whether STBC is used or not, for each individual STA) may not
be included in HE-SIG-A field. Although the individual parameters
may be included in HE-SIG-B field, information about the number of
spatial streams and information indicating whether STBC is used or
not, need to be transmitted before a HE-LTF field because the
number of spatial streams and the information indicating whether
STBC is used or not are significant to determination of
configuration information about a preamble and a PSDU in a HE PPDU
frame format (e.g., the number of HE-LTF elements is determined
according to a combination of the number of spatial streams and the
information indicating whether STBC is used or not). For this
purpose, a HE PPDU frame format as illustrated in FIG. 13 may be
used for a UL HE PPDU transmission.
[0171] FIG. 13 depicts another exemplary HE PPDU frame format
according to the present disclosure. The HE PPDU frame format
illustrated in FIG. 13 is characterized in that a structure of
HE-SIG-A, HE-SIG-B, and HE-SIG-C fields similar to in FIG. 12 is
used for a UL PPDU transmission.
[0172] As described before, if a UL MU-MIMO-mode or OFDMA-mode
transmission is performed by triggering of an AP (according to
common/individual parameters provided by the AP), an individual STA
may not need to report an individual parameter to the AP. In this
case, one or more of a HE-SIG-B field, a HE-SIG-C field, and a
first HE-LTF element (i.e., a HE-LTF between a HE-STF field and a
HE-SIG-B field) illustrated in FIG. 13 may not exist. In this case,
a description of each field given below may be applied only in the
presence of the field.
[0173] In the example of FIG. 13, a HE-SIG-A field is transmitted
per channel (i.e., per 20-MHz channel) and may include transmission
parameters common to simultaneously transmitted HE PSDUs. Since the
same information is transmitted in up to HE-SIG-A fields in UL
PPDUs transmitted by HE STAs allocated to subchannels, the AP may
receive the same signals from the plurality of STAs
successfully.
[0174] A HE-SIG-B field is transmitted per subchannel in one
channel. The HE-SIG-B field may have an independent parameter value
according to the transmission characteristics of a HE PSDU
transmitted on each subchannel. The HE-SIG-B field may include
spatial stream allocation information and information indicating
whether STBC is used or not, for each subchannel. If MU-MIMO is
applied to a subchannel (i.e., if a plurality of STAs perform
transmission on a subchannel), the HE-SIG-B field may include a
common parameter for the plurality of STAs paired on the
subchannel.
[0175] A HE-SIG-C field is transmitted on the same subchannel as
the HE-SIG-B field and may include information about an MCS and a
packet length. If MU-MIMO is applied to a subchannel (i.e., if a
plurality of STAs perform transmission on a subchannel), the
HE-SIG-C field may include respective individual parameters for
each of the plurality of STAs paired on the subchannel.
[0176] Similarly to DL MU-MIMO-mode or OFDMA-mode HE PPDU
transmission, transmissions of PSDUs may start at different time
points on subchannels in UL MU-MIMO-mode or OFDMA-mode HE PPDU
transmission, and if OFDM symbols are not aligned accordingly, then
the implementation complexity of an AP that receives a plurality of
PSDUs increased. To solve this problem, `the number of HE-LTFs may
be determined for all subchannels according to the maximum of the
numbers of HE LTFs required according to the total numbers of
spatial streams transmitted on each subchannel for a set of HE STAs
allocated to each of subchannels` as described with reference to
the example of FIG. 11.
[0177] This feature may mean that the HE-LTF field start at the
same time point and end at the same time point across all users
(i.e., HE STAs) in UL MU-MIMO-mode or OFDMA-mode transmission. Or
it may be said that the HE-LTF sections of a plurality of
subchannels have the same length across all HE STAs in UL
MU-MIMO-mode or OFDMA-mode transmission. Or it may be said that
each of the HE-LTF sections of a plurality of subchannels includes
the same number of HE-LTF elements across all HE STAs in UL
MU-MIMO-mode or OFDMA-mode transmission. Therefore, PSDU
transmission timings are synchronized between a plurality of
subchannels across all HE STAs in UL MU-MIMO-mode or OFDMA-mode
transmission.
[0178] As described before, a plurality of STAs may simultaneously
transmit PSDUs in a HE PPDU frame format on their allocated
subchannels or on their allocated spatial streams to an AP (i.e.,
referred to as UL MU-MIMO or OFDMA transmission or "UL MU
transmission") and may simultaneously receive PSDUs in the HE PPDU
frame format on their allocated subchannels on their allocated
spatial streams from the AP (i.e., referred to as DL MU-MIMO or
OFDMA transmission or "DL MU transmission").
[0179] Now, a description will be given below of a UL MU
transmission method according to the present disclosure. For
example, specific examples of triggering for UL MU transmission, a
transmission time of a UL MU PPDU, an ACK for UL MU transmission,
error recovery for UL MU transmission, and UL MU triggering
supporting random access for UL MU transmission will be
described.
[0180] UL MU-MIMO transmission is taken as an example of UL MU
transmission in the following examples of the present disclosure.
However, the examples of the present disclosure is also applicable
in the same manner to UL OFDMA transmission in which one
transmission channel is divided into a plurality of subchannels and
each STA performs simultaneous UL transmission on an allocated
subchannel. That is, UL MU transmission includes UL MU-MIMO
transmission or UL OFDMA transmission in the following
description.
[0181] FIG. 14 depicts an exemplary frame exchange sequence
including UL MU transmission according to the present
disclosure.
[0182] The AP may transmit a poll frame for UL MU transmission
(i.e., a UL MU trigger frame) to STAs to which UL MU transmission
has been granted or requested. To request UL MU transmission from
STA1, STA2, STA3, and STA4, the AP may transmit a UL MU Poll frame
to STA1, STA2, STA3, and STA4. The UL MU poll frame directed to the
plurality of STAs may include Receiver Address (i.e., an Address 1
field in a MAC header) set to a broadcast address, Transmitter
Address (i.e., an Address 2 field in the MAC header) set to the MAC
address of the AP, Basic Service Set Identifier (BSSID), and
payload with IDs (e.g., Association Identifiers (AIDs) of the STAs
requested to perform the UL MU transmission. The UL MU Poll frame
may further include information about a transmission time (length)
of a UL MU PPDU to be transmitted simultaneously by the STAs.
[0183] Upon receipt of the UL MU Poll frame (i.e., a poll frame
triggering UL MU transmission (UL MU-MIMO transmission or UL OFDMA
transmission)), the STAs may determine whether they are requested
for the UL MU transmission based on information included in the UL
MU Poll frame (e.g., UL MU triggering information). If an STA
determines that it is requested for the UL MU transmission, the STA
may transmit a UL MU PPDU to the AP during a given time period
indicated by the information about the transmission time of the UL
MU PPDU (i.e., UL MU-MIMO PPDU or UL OFDMA PPDU), included in the
UL MU Poll frame.
[0184] To align the transmission times of the UL MU PPDU
simultaneously transmitted by the plurality of STAs, each of the
STAs may include a padding in a UL MU PPDU that it transmits. That
is, the STA may determine the transmission time of the UL MU PPDU
(or the length of the UL MU PPDU) based on the information about a
transmission time included in the poll frame eliciting transmission
of the UL MU PPDU, determine whether to include a padding in the UL
MU PPDU based on the determined UL MU PPDU transmission time (or UL
MU PPDU length), and determine the length of the padding when the
padding is to be included.
[0185] Specifically, since the plurality of STAs, which
simultaneously transmit the UL MU PPDU, may differ in data length,
the STAs may include paddings in the UL MU PPDU in order to prevent
the increase of processing complexity of a UL MU PPDU receiver in
case the UL transmissions end at different time points in different
resources (e.g., subchannels or streams) allocated to the plurality
of STAs, or to protect the UL MU PPDU from a third-party STA.
[0186] The padding may include a MAC padding or a PHY padding. The
MAC padding includes adding as many padding bits as a required size
after an MPDU including actual payload at the MAC layer. For
example, an MPDU (i.e., an A-MPDU subframe) of a predetermined size
may be added after an MPDU including actual payload. The MPDU
(i.e., the A-MPDU subframe) of the predetermined size added for the
MAC padding may correspond to one or more 4-octet MPDUs (or A-MPDU
subframes) having null data (e.g., a zero-octet MSDU). The PHY
padding is a padding used to match the number of coded bits of the
last OFDM symbol to a specific criterion (e.g., a parameter value
for coded bits per OFDM symbol (i.e., N.sub.CBPS)), when an A-MPDU
is configured into one PSDU at the PHY layer. The number of bits
added as the padding may be 8 (i.e., 1 octet) or smaller.
[0187] In the example of FIG. 14, STA1 has data to be transmitted
during a transmission time indicated by a poll frame triggering UL
MU transmission. Then, STA1 may transmit a UL MU PPDU with only a
PHY padding, without a MAC padding. In contrast, STA2, STA3, and
STA4 do not have data to be transmitted during the transmission
time indicated by the UL MU Poll frame. Then, each of STA2, STA3,
and STA4 may determine the length of a MAC padding based on the
amount of data to be transmitted, apply the MAC padding, and then
apply a PHY padding, thus performing the UL MU PPDU transmission.
Therefore, the transmission times of the UL MU PPDU transmitted by
STA1, STA2, STA3, and STA4 may be aligned with one another. That
is, transmissions of all of the STAs may end at a time point
indicated by the UL MU Poll frame (or UL MU trigger frame) in the
UL MU PPDU.
[0188] Further, in a UL MU PPDU in which transmissions of a
plurality of STAs have the same transmission time (or end at the
same time point), a transmission scheme of an ACK for the UL MU
PPDU may be indicated by an ACK Policy field included in the MAC
header of data transmitted by the plurality of STAs. For example,
if the ACK Policy is set to Immediate Block ACK, a data receiving
STA may transmit a block ACK frame immediately, for example, an
SIFS after the UL MU PPDU transmission ends. Or in the case where
the ACK Policy is set to Delayed Block ACK, if a data transmitting
STA transmits a block ACK request frame to a data receiving STA
after data transmission ends, the data receiving STA may transmit a
frame including a block ACK in response to the block ACK request
frame.
[0189] According to the present disclosure, one or more of STAs
that simultaneously transmit data units may set the ACK Policies to
Immediate Block ACK. If a plurality of STAs that simultaneously
transmit data units set the ACK Policies commonly to Immediate
Block ACK, the AP may simultaneously transmit ACKs (e.g., a block
ACK) in response to the data units simultaneously transmitted by
the plurality of STAs. If the ACK Policies of a first group
including a part of the plurality of STAs that simultaneously
transmit data units (e.g., an STA group including one or more STAs)
are set to Immediate Block ACK and the ACK Policies of a second
group (e.g., including the other STA(s) except for the STA(s) of
the first group) are set to Delayed Block ACK, the AP may
sequentially transmit an ACK(s) for the data unit(s) transmitted by
the STA(s) of the second group after transmitting ACKs for a data
unit(s) transmitted by the STA(s) of the first group.
[0190] Upon receipt of UL MU transmission from the plurality of
STAs, the AP may transmit ACK information for the received UL MU
PPDU to the plurality of STAs. Information triggering UL MU
transmission of the plurality of STAs may be transmitted along with
the ACK information for the plurality of STAs. For example, a block
ACK frame may further include information triggering additional UL
MU transmission or a poll frame triggering additional UL MU
transmission may further include the ACK information. That is, the
AP may transmit the poll frame triggering UL MU transmission and
the block ACK frame in one PPDU.
[0191] FIG. 15 depicts another exemplary frame exchange sequence
including UL MU transmission according to the present
disclosure.
[0192] In the example of FIG. 15, it is assumed that STA1 fails to
receive a poll frame triggering UL MU transmission from STA1, STA2,
STA3, and STA4. STA1 that has failed to receive the UL MU Poll
frame may not participate in the UL MU transmission, whereas only
STA2, STA3, and STA4 may simultaneously transmit a UL MU PPDU.
[0193] In the UL MU transmission, STA2, STA3, and STA4 may apply
MAC paddings based on a transmission time indicated by the UL MU
Poll frame. Because a MAC padding applied by each of STA2, STA3,
and STA4 is based on the transmission time of UL MU transmission
including transmission of STA1, the MAC padding transmission
periods of STA2, STA3, and STA4 do not include meaningful data
transmission, unnecessarily occupying a wireless medium in UL MU
transmission except for transmission of STA1. That is, if the other
STAs apply MAC paddings to a UL MU PPDU in a situation in which a
part (e.g., STA1) of a plurality of STAs has enough data to be
transmitted during a transmission period given to the STAs by a UL
MU Poll frame does not participate in UL MU transmission, system
performance may be degraded.
[0194] FIG. 16 depicts another exemplary frame exchange sequence
including UL MU transmission according to the present
disclosure.
[0195] In the example of FIG. 16, it is assumed that STA1 fails to
receive a poll frame triggering UL MU transmission of STA1, STA2,
STA3, and STA4. STA1 that has failed to receive the UL MU Poll
frame may not participate in the UL MU transmission, whereas only
STA2, STA3, and STA4 may simultaneously transmit a UL MU PPDU.
[0196] FIG. 16 illustrates an exemplary case in which a plurality
of STAs are allowed to have different UL MU PPDU transmission times
(or different UL MU PPDU lengths) in UL MU transmission of the STAs
triggered by a UL MU Poll frame. That is, different transmission
times of a UL MU PPDU for a plurality of STAs may mean that
transmission times of legacy preambles (e.g., L-STFs, L-LTFs, and
L-SIGs) and transmission times of HE preambles (e.g., HE-SIG-As,
HE-SIG-Bs, HE-STFs, HE-LTFs, etc.) are aligned among the plurality
of STAs and data (e.g., PSDUs) starts at the same time point but
ends at different points for the plurality of STAs in the UL MU
PPDU. Also, different transmission times of a UL MU PPDU for a
plurality of STAs may mean that the plurality of STAs do not apply
MAC paddings. However, the plurality of STAs may apply PHY paddings
for transmission of the UL MU PPDU.
[0197] Further, if different UL MU PPDU transmission times are
allowed for a plurality of STAs, even though a poll frame
triggering UL MU transmission includes information about a UL MU
PPDU transmission time (or a UL MU PPDU length), the plurality of
STAs may not apply MAC paddings based on the information about the
UL MU PPDU transmission time. However, an STA(s) performing the UL
MU transmission may perform the UL MU PPDU transmission within the
UL MU PPDU transmission time indicated by the UL MU Poll frame.
[0198] As described above, even though a part of a plurality of
STAs whose UL MU transmission is triggered by a UL MU Poll frame do
not perform the UL transmission, if the other STA(s) does not apply
a MAC padding to transmission of a UL MU PPDU, degradation of
system performance caused by an unnecessary MAC padding may not
occur.
[0199] In addition, in the case where a part of a plurality of STAs
whose UL MU transmission is triggered by a UL MU Poll frame do not
perform the UL transmission and the UL MU PPDU transmission time of
the other STA(s) is changed, if the ACK Policy of the other STA(s)
is set to Immediate Block ACK, it may be ambiguous for the AP to
determine an STA whose ending time of a UL MU PPDU is a time when
ACK information is to be transmitted in response to the UL MU PPDU.
Moreover, since each of the plurality of STAs participating in the
UL MU transmission does not have knowledge of the ending times of
UL MU transmission of the other STAs except for the STA, the STA
does not determine when it will receive a frame including ACK
information in response to the UL MU transmission. That is, if a
plurality of different UL MU PPDU transmission times are allowed,
each of the plurality of STAs whose UL MU transmission is triggered
may not expect an immediate control response after transmitting the
UL MU PPDU and may not define a timer and a timeout procedure for
the control response frame. Accordingly, if a plurality of
different UL MU PPDU transmission times are allowed, the ACK Policy
of each of the plurality of STAs may be set to Delayed Block ACK
instead of Immediate Block ACK.
[0200] Now, a detailed description will be given of an operation
for transmitting a block ACK frame by an AP receiving a UL MU
PPDU.
[0201] The AP may determine a transmission time of a block ACK
frame to be after an SIFS from, for example, the ending time of
reception of the last data unit of a UL MU PPDU (e.g., a time when
the PHY layer invokes a PHY-RXEND.Indication primitive to the MAC
layer), commonly in both the cases where the ACK Policies of data
units from one or more of a plurality of STAs transmitting a UL MU
PPDU are set to Immediate Block ACK as illustrated in FIGS. 14 and
15 and to Delayed Block ACK as illustrated in FIG. 16. However, the
ending times of data units received from a plurality of STAs
coincide with a time indicated by a UL MU Poll frame (or a UL MU
trigger frame) in the case of FIGS. 14 and 15, whereas the ending
times of data units received from a plurality of STAs may be
different in the case of FIG. 16. In consideration of this aspect,
the AP may determine the reception completion time of a UL MU
PPDU.
[0202] In regard to this, an error recovery procedure for the UL MU
transmission triggering procedure will be described. When
transmitting a poll frame triggering UL MU transmission, the AP may
activate a UL MU poll timer until the AP starts to receive a UL MU
PPDU. The UL MU poll timer expires at a time point when a time
period corresponding to a UL MU Poll timeout elapses. If the AP
receives a valid start (e.g. a valid PHY header) of a UL MU PPDU
within a UL MU Poll timeout, the PHY of the AP may invoke the
PHY-RXSTART.Indication primitive to the MAC.
[0203] If the PHY-RXSTART.Indication primitive is invoked within
the UL MU Poll timeout, the AP may consider that at least one of
STAs requested for the UL MU transmission has started to transmit a
UL MU PPDU. That is, if the AP receives a data unit (e.g., an MPDU)
from at least one STA indicated by polling for UL MU transmission
(or UL MU triggering), the AP may determine that it has started to
receive the UL MU transmission successfully. That is, if the AP
receives a data unit (e.g., an MPDU) from at least one STA
indicated by polling for UL MU transmission (or UL MU triggering),
the AP may determine that frame exchange initiated by the UL MU
polling (or UL MU triggering) is successful.
[0204] On the other hand, if the PHY-RXSTART.Indication primitive
has not been invoked within the UL MU Poll timeout, the AP may
perform the error recovery procedure, determining that an error has
occurred to the polling procedure for triggering UL MU
transmission, which will be described with reference to FIG.
17.
[0205] Meanwhile, when determining whether transmission of a UL MU
PPDU has been completed, the AP may invoke the PHY-RXEND.Indication
primitive. The PHY-RXEND.Indication primitive corresponds to
indication information indicating to a local MAC entity that a
current PSDU has been completely received by the PHY. This
primitive provides parameters as listed in [Table 4] below.
TABLE-US-00004 TABLE 4 PHY-RXEND.indication( RXERROR, RXVECTOR
)
[0206] In [Table 4], an RXERROR parameter may deliver at least one
of values indicating NoError, FormatVioloation, CarrierLost, and
UnsupportedRate. After a receive state machine of the PHY detects
what looks like a valid preamble and Start Frame Delimiter (SFD), a
plurality of error conditions may occur. The following parameters
are returned for the respective error conditions. [0207] NoError.
This value is used to indicate that no error has occurred during a
reception process at the PHY. [0208] FormatViolation. This value is
used to indicate that there is an error in the format of a received
PPDU. [0209] CarrierLost. This value is used to indicate that a
carrier cannot be found during reception of an incoming PSDU and
thus PSDU processing cannot be performed any longer. [0210]
UnsupportedRate. This value is used to indicate that an unsupported
data rate has been detected during reception of an incoming PPDU.
[0211] Filtered. This value is used to indicate that an incoming
PPDU has been filtered out due to a condition set by
PHYCONFIG_VECTOR during reception of the incoming PPDU.
[0212] In [Table 4], RXVECTOR represents a list of parameters
provided to the local MAC entity by the PHY, when the PHY receives
a valid PHY header or the last PSDU data bit of a received frame.
Only if a dot11RadioMeasurementActivated parameter is set to True,
RXVECTOR is included. RXVECTOR may include all of MAC parameters
and MAC management parameters.
[0213] A PHY-RXEND.Indication primitive may be generated to
indicate to the local MAC entity that the receive state machine of
the PHY has completed reception with or without an error. In the
presence of Signal Extension, the PHY-RXEND.Indication primitive
may be generated at the ending point of the Signal Extension.
[0214] If the value of RXERROR is NoERROR, the MAC may use the
PHY-RXEND.Indication primitive as a reference for a channel access
timing.
[0215] Upon receipt of a UL MU PPDU from a plurality of STAs, the
AP may determine one reception starting time based on reception
starting times of the PPDU from the STAs and one reception ending
time based on reception ending times of data units (e.g., PSDUs)
from the STAs. For this purpose, the PHY of the AP may determine
one reception starting time or one reception ending time, or the
MAC of the AP may determine one reception starting time or one
reception ending time.
[0216] Specifically, upon receipt of a UL MU PPDU from a plurality
of STAs, the AP may invoke one PHY-RXSTART.Indication primitive and
one PHY-RXEND.Indication primitive from the PHY to the MAC. For
example, the PHY may invoke the PHY-RXSTART.Indication primitive at
one reception starting time (e.g., at one common reception starting
time if the UL MU PPDU is received at the same starting time from
the plurality of STAs as illustrated in the example of FIGS. 14 and
15, or at one (e.g., the last) of different reception starting
times of the UL MU PPDU from the plurality of STAs as illustrated
in the example of FIG. 16) based on time points at which data units
start to be received from the plurality of STAs. Also, the PHY may
invoke the PHY-RXEND.Indication primitive at one reception ending
time (e.g., at one common reception ending time if the UL MU PPDU
reception is completed at the same time point from the plurality of
STAs as illustrated in the example of FIGS. 14 and 15, or at one
(e.g., the last) of different reception ending times of the UL MU
PPDU from the plurality of STAs as illustrated in the example of
FIG. 16) based on time points at which the data units are
completely received from the plurality of STAs.
[0217] Or the PHY of the AP may invoke individual
PHY-RXSTART.Indication primitives and individual
PHY-RXEND.Indication primitives to the MAC, for the UL MU PPDU
received from the plurality of STAs. That is, the PHY may invoke a
plurality of PHY-RXSTART.Indication primitives corresponding to the
respective starting times of PPDU reception from the plurality of
STAs to the MAC, and the MAC may determine one of them (e.g., one
common reception starting time or the last reception starting time)
to be a PPDU reception starting time. Also, the PHY may invoke a
plurality of PHY-RXEND.Indication primitives corresponding to the
respective ending times of PPDU reception from the plurality of
STAs to the MAC, and the MAC may determine one of them (e.g., one
common reception ending time or the last reception ending time) to
be a PPDU reception ending time.
[0218] If the AP has completely received PSDUS from all STAs
transmitting the UL MU PPDU in this manner, the AP may determine a
time point at which the PHY-RXEND.Indication is invoked to be an
ending time of the UL MU PPDU reception. Accordingly, the AP may
transmit a block ACK frame an SIFS after the ending time of the UL
MU PPDU reception. For example, a PHY-RXEND.Indication primitive
corresponding to one common ending time of PSDU reception from a
plurality of STAs may be invoked and a block ACK frame may be
transmitted an SIFS after the invocation time of the
PHY-RXEND.Indication primitive in the case of FIGS. 14 and 15. In
the case of FIG. 16, although PSDU reception from a plurality of
STAs ends at different time points, a PHY-RXEND.Indication
primitive corresponding to the last of the ending times may be
invoked and a block ACK frame may be transmitted an SIFS after the
invocation time.
[0219] If the RXERROR parameter of a data unit received from at
least one of all STAs transmitting the UL MU PPDU is set to
NoERROR, the AP may transmit a block ACK frame to the STAs.
[0220] For example, upon receipt of a UL MU PPDU including data
units simultaneously transmitted from STA1, STA2, STA3, and STA4,
the AP may confirm that the ACK Policies of STA1, STA2, STA3, and
STA4 are Immediate Block ACK and the PHY of the AP may transmit a
block ACK frame an SIFS after the ending time of the UL MU PPDU
(e.g., a common time point at which the data units of STA1, STA2,
STA3, and STA4 end) in the example of FIG. 14. Herein, if the
RXERROR parameter of at least one of the data units received from
STA1, STA2, STA3, and STA4 is set to NoERROR, the AP may transmit a
block ACK frame. For example, the block ACK frame may include ACK
information for the data units received from STA1, STA2, STA3, and
STA4.
[0221] In the example of FIG. 15, upon receipt of a UL MU PPDU
including data units simultaneously transmitted from STA2, STA3,
and STA4, the AP may confirm that the ACK Policies of STA2, STA3,
and STA4 are Immediate Block ACK and transmit a block ACK frame an
SIFS after the ending time of reception of the UL MU PPDU at the
PHY (e.g., a common ending time of the data units from STA2, STA3,
and STA4). If the RXERROR parameter of at least one of the data
units transmitted from STA2, STA3, and STA4 is set to NoERROR, the
AP may transmit the block ACK frame. For example, the block ACK
frame may include ACK information for the data units transmitted
from STA2, STA3, ad STA4. Or the block ACK frame may include ACK
information for STA1 STA2, STA3, and STA4 requested for the UL MU
transmission (in this case, ACK information for STA1 may indicate
failure of data reception from STA1).
[0222] In the example of FIG. 16, upon receipt of a UL MU PPDU
including data units simultaneously transmitted from STA2, STA3,
and STA4, the AP may confirm that the ACK Policies of STA2, STA3,
and STA4 are Delayed Block ACK and transmit a block ACK frame an
SIFS after the ending time of reception of the last UL MU PPDU at
the PHY (e.g., a time at which a PHY-RXEND.Indication primitive is
generated). If the RXERROR parameter of at least one of the data
units transmitted from STA2, STA3, and STA4 is set to NoERROR, the
AP may transmit the block ACK frame. For example, the block ACK
frame may include ACK information for the data units transmitted
from STA2, STA3, ad STA4. Or the block ACK frame may include ACK
information for STA1 STA2, STA3, and STA4 requested for the UL MU
transmission (in this case, ACK information for STA1 may indicate
failure of data reception from STA1).
[0223] Meanwhile, to protect a UL MU PPDU transmitted by a
plurality of STAs (e.g., STA2, STA3, and STA4) in the example of
FIG. 16, duration information included in the legacy preamble
(e.g., an L-SIG field) of the UL MU PPDU may be set to a value
(e.g., a time corresponding to an L-SIG Duration in FIG. 16)
covering at least a remaining transmission time after transmission
of the legacy preamble of the UL MU PPDU and a time at which a
block ACK frame starts to be transmitted in response to the UL MU
PPDU (i.e., a time at which a valid PLCP header of the block ACK
frame is transmitted). Thus, a third-party STA may check the legacy
preamble of the UL MU PPDU and set a NAV so that a medium may be
regarded as busy during a time period indicated by the L-SIG
Duration. In the example of FIG. 16, the value of duration
information of the L-SIG of STA2 transmitting the longest data unit
may be largest and the NAV of the third-party STA may be set
according to the value of the duration information of the L-SIG of
STA2.
[0224] FIG. 17 depicts another exemplary frame exchange sequence
including UL MU transmission according to the present
disclosure.
[0225] FIG. 17 illustrates a procedure for recovering UL MU polling
(or UL MU triggering), when an AP transmits a UL MU Poll frame and
a PHY-RXSTART.Indication primitive is not invoked during a UL MU
Poll timeout. If the PHY-RXSTART.Indication primitive is not
invoked during the UL MU Poll timeout period, the AP may determine
whether a channel is idle during a specific IFS (referred to as an
xIFS which may correspond to, for example, a PIFS or AIFS[i]) by
CCA. If the channel is idle, the AP may transmit an additional UL
MU Poll frame to STAs.
[0226] Hereinbelow, examples of UL MU triggering supporting random
access for UL MU transmission according to the present disclosure
will be described.
[0227] Basically, UL MU transmission may be performed by UL MU
polling (or UL MU triggering) of the AP. That is, STAs that will
perform UL MU transmission may be selected by a poll frame
triggering the UL MU transmission (or a UL MU trigger frame)
provided by the AP, resources for the UL MU transmission (e.g., a
UL MU transmission time and subchannels or streams used for the UL
MU transmission) may be allocated, and the plurality of STAs may
perform the UL MU transmission based on the allocated
resources.
[0228] Meanwhile, random access for UL MU transmission means that
STAs unspecified by an AP perform UL MU transmission or a plurality
of STAs perform UL MU transmission using resources unspecified by
the AP. An STA performing the UL MU random access may be any of
predetermined STA candidates and the resources used for the UL MU
random access may be any of predetermined resource candidates. That
is, the candidate STAs or candidate resources for the UL MU random
access may be predetermined and the UL MU random access may be
performed by any of the candidates STAs or using any of the
candidate resources.
[0229] In an example of UL MU random access according to the
present disclosure, a UL MU Poll Request frame and a UL MU Poll
Response frame may be defined and used. The UL MU Poll Request
frame may correspond to a frame triggering (or eliciting) UL MU
random access of a plurality of STAs, and the UL MU Poll Response
frame may correspond to a frame transmitted by each of the
plurality of STAs by UL MU random access. Also, STAs that will
participate in UL MU PPDU transmission (e.g., STAs having data to
be transmitted to an AP) may be predetermined through exchange
between a UL MU Poll Request frame and UL MU Poll Response
frames.
[0230] The examples of the present disclosure regarding a UL MU
PPDU transmission time provided by UL MU transmission triggering
information, an ACK for UL MU transmission, and error recovery for
UL MU transmission as described before are applicable to a
plurality of frames transmitted by UL MU random access. The
description of a poll frame triggering UL MU transmission in the
foregoing examples is applicable to a frame triggering UL MU random
access (e.g., a UL MU Poll Request frame), and the description of
UL MU transmission elicited by a poll frame triggering the UL MU
transmission and an ACK transmitted in response to the poll frame
is applicable to a frame transmitted by UL MU random access (e.g.,
a UL MU Poll Response frame) and an ACK (e.g., a UL MU Poll Confirm
frame or a block ACK frame) transmitted in response to the
frame.
[0231] To trigger UL MU random access, the AP may broadcast a UL MU
Poll Request frame. That is, destination STAs are not specified for
the UL MU Poll Request frame. Rather, any STA may receive the UL MU
Poll Request frame. Among STAs receiving the UL MU Poll Request
frame, an STA having a data frame to be transmitted to the AP
(i.e., an STA to participate in transmission of a UL MU PPDU) may
transmit a UL MU Poll Response frame to the AP. The UL MU Poll
Response frame may be transmitted in immediate response to the UL
MU Poll Request frame (i.e., the STA may transmit the UL MU Poll
Response frame an SIFS after receiving the UL MU Poll Request
frame).
[0232] If a plurality of STAs transmit such UL MU Poll Response
frames, the UL MU Poll Response frames may be configured in a UL MU
PPDU format. For example, a UL MU Poll Response frame may have a
fixed frame size and to minimize protocol overhead caused by
collision, the UL MU Poll Response frame may have a small frame
size. For example, the UL MU Poll Response frame may have a control
frame format. Also, the UL MU Poll Response frame may include
identification information (e.g., a MAC address or an AID) of the
transmitting STA (i.e., an STA to participate in the UL MU PPDU
transmission), information about a buffer status, and information
about resources to be used for the UL MU PPDU transmission (e.g. a
resource unit, a subchannel, or the number of space-time
streams).
[0233] FIGS. 18 and 19 depict exemplary exchanges of a UL MU Poll
Request frame, a UL MU Poll Response frame, and a UL MU Poll
Confirm frame according to the present disclosure.
[0234] If the AP broadcasts a UL MU Poll Request frame, STAs that
will participate in UL MU PPDU transmission may receive the UL MU
Poll Request frame and transmit UL MU Poll Response frames to the
AP an SIFS later. In the examples of FIGS. 18 and 19, it is assumed
that an AP is capable of receiving a UL MU PPDU simultaneously from
a plurality of STAs in four distinguished resources (e.g., four
subchannels or four space-time streams). If one STA uses one
resource, up to four STAs may participate in the UL MU PPDU
transmission.
[0235] As illustrated in the example of FIG. 18, if four STAs
simultaneously transmit UL MU Poll Response frames, each STA using
one resource (e.g., one resource unit or one space-time stream),
the AP may identify the STAs that want to participate in UL MU PPDU
transmission by receiving the UL MU Poll Response frames from the
four STAs. Thus, the AP may transmit a UL MU Poll Confirm frame to
STA1, STA2, STA3, and STA4 an SIFS after receiving the UL MU Poll
Response frames. The UL MU Poll Confirm frame may correspond to a
poll frame triggering UL MU transmission in the foregoing examples.
Upon receipt of the UL MU Poll Confirm frame, STA1, STA2, STA3, and
STA4 may perform the UL MU PPDU transmission based on trigger
information provided by the AP. The ACK Policy of a data unit from
each of the plurality of STAs, included in the UL MU PPDU may be
set to Block ACK. Accordingly, the plurality of STAs may attempt to
receive a block ACK frame from the AP an SIFS after transmitting
the UL MU PPDU.
[0236] The example of FIG. 19 illustrates a case where more STAs
than the AP may support for UL MU transmission respond to a UL MU
Poll Request frame. For example, if each STA uses one resource
(e.g., one subchannel or one space-time stream), the AP may receive
UL MU transmission from four STAs simultaneously in four
distinguished resources. If five STAs (e.g., STA1, STA2, STA3,
STA4, and STA5) out of the STAs receiving the broadcast UL MU Poll
Request frame transmit UL MU Poll Response frames, the AP may not
receive the UL MU Poll Response frames successfully. That is, a
plurality of STAs may perform UL MU random access according to a UL
MU Poll Request frame. Transmissions of some STAs may collide
during random access. In this case, the AP may not successfully
receive UL MU transmission in the random access scheme. Therefore,
the AP may broadcast an additional UL MU Poll Request frame after a
UL MU Poll Request timeout. If four STAs (e.g., STA1, STA2, STA3,
and STA4) transmit UL MU Poll Response frames, the AP may receive
the UL MU Poll Response frames successfully and then transmit a UL
MU Poll Confirm frame to the four STAs. Therefore, the four STAs
may perform UL MU PPDU transmission and attempt to receive a block
ACK frame.
[0237] Herein, a frame triggering simultaneous UL transmission
(i.e., UL MU random access) of arbitrary STAs (e.g., a UL MU Poll
Request frame) may include response condition information. A
response condition may include the AC of UL data, a buffer size,
etc. If the AP broadcasts a second UL MU Poll Request frame after a
timeout occurs for a transmitted first UL MU Poll Request frame, a
second response condition included in the second UL MU Poll Request
frame may be reinforced or limited compared to a first response
condition included in the first UL MU Poll Request frame. For
example, the number of STAs satisfying the second response
condition may be set to be smaller than the number of STAs
satisfying the first response condition. The example of FIG. 19
corresponds to a case in which although STA1, STA2, STA3, STA4, and
STA5 satisfy the first response condition included in the first UL
MU Poll Request frame, only STA1, STA2, STA3, and STA4 except for
STA5 satisfy the second response condition included in the second
UL MU Poll Request frame.
[0238] Further, a frame triggering UL MU random access may include
information about responding STA candidates or resource candidates
as a response condition for the frame. STAs satisfying the response
condition may transmit response frames (e.g., UL MU Poll Response
frames) by UL MU random access. If the AP fails to receive the
response frames due to collision between transmissions of the
response frames, the AP may transmit a frame triggering additional
UL MU random access by reinforcing or limiting the response
condition.
[0239] Also, a response frame transmitted in the UL MU random
access scheme by an STA receiving the frame triggering UL MU random
access may include information about the buffer status of the
responding STA, a property of UL data (e.g., AC), or UL data.
[0240] FIG. 20 depicts UL MU random access of STAs operating in
power save mode according to the present disclosure.
[0241] In the presence of data (i.e., DL data) buffered in the AP
for transmission to an STA operating in the power save mode, the
STA may transmit signaling information indicating that it has
switched from a doze state to an awake state and requesting DL data
(the signaling information may be included in a poll frame
requesting DL data (e.g., a Power Save (PS)-Poll frame or a trigger
frame triggering a service period, and this poll frame is
distinguished from a poll frame or trigger frame triggering UL MU
transmission) to the AP based on a Traffic Indication Map (TIM)
included in a beacon frame or the like. The STA operating in the
power save mode may also operate in doze mode or awake mode to save
power. Hereinbelow, an STA operating in the power save mode is
referred to as a TIM STA.
[0242] To support UL MU random access of a TIM STA, the AP may
broadcast a frame triggering UL MU random access (e.g., a UL MU
Poll Request frame) for TIM STAs. For example, a response condition
included in the frame triggering UL MU random access may be set to
limit responding STA candidates to TIM STAs. Upon receipt of the
frame triggering UL MU random access, an STA may transmit a PS-Poll
frame or trigger frame requesting DL data to the AP in UL MU.
[0243] For example, the frame triggering UL MU random access of a
plurality of TIM STAs by the AP may correspond to a UL MU Poll
Request frame, and the PS-Poll frames requesting DL data (or the
trigger frame triggering a service period) transmitted
simultaneously by the plurality of STAs may correspond to UL MU
Poll Response frames. To indicate that a UL MU Poll Response frame
corresponds to a PS-Poll frame requesting DL data (or a trigger
frame triggering a service period), an End of Service Period (EOSP)
field of the UL MU Poll Response frame (e.g., the EOSP field may be
included in the QoS Control field of a MAC header) may be set to 0.
That is, a UL MU Poll Response frame with an EOSP field set to 0
may execute the same function or play the same role as a PS-Poll
frame requesting DL data by a TIM STA (or a trigger frame
triggering a service period). Upon receipt of the UL MU Poll
Response frame with the EOSP field set to 0, the AP may transmit
information indicating successful reception of the UL MU Poll
Response frames (i.e., PS-Poll frames requesting DL data (or
trigger frames triggering a service period) from a plurality of
STAs to the STAs by transmitting a UL MU Poll Confirm frame or a
block ACK frame to the plurality of TIM STAs.
[0244] In the example of FIG. 20, the AP may elicit transmissions
of UL MU Poll Response frames (i.e., PS-Poll frames requesting DL
data or trigger frames triggering a service period) from TIM STAs
by random access by broadcasting a UL MU Poll Request frame. For
this purpose, signaling information indicating that a destination
STA of the UL MU Poll Request frame (or an STA allowed to respond
to the UL MU Poll Request frame) is a TIM STA operating in the
power save mode may be included in the UL MU Poll Request
frame.
[0245] Among TIM STAs receiving the UL MU Poll Request frame, TIM
STAs determining to request DL data (or to trigger a service
period) may transmit UL MU Poll Response frames each with an EOSP
field set to 0 to the AP an SIFS after receiving the UL MU Poll
Request frame. In the example of FIG. 20, STA1, STA2, STA3, and
STA4 among a plurality of TIM STAs determine to request DL data (or
trigger a service period) and simultaneously transmit UL MU Poll
Response frames to the AP.
[0246] Upon receipt of the UL MU Poll Response frames each having
an EOSP field set to 0 from STA1, STA2, STA3, and STA4, the AP may
consider the received UL MU Poll Response frames to be PS-Poll
frames requesting DL data (or trigger frames triggering a service
period) and transmit a UL MU Poll Confirm frame or a block ACK
frame to STA1, STA2, STA3, and STA4 in order to acknowledge
reception of the UL MU Poll Response frames.
[0247] Upon confirmation of successful reception of the UL MU Poll
Response frames (i.e., the PS-Poll frames requesting DL data or the
trigger frames triggering a service period) at the AP, the TIM STAs
may be kept in the awake state to receive DL frames buffered in the
AP. While the TIM STAs are in the awake state, the AP may
simultaneously transmit a DL MU PPDU (i.e., a DL MU-MIMO PPDU or a
DL OFDMA PPDU) including the DL data buffered for the plurality of
TIM STAs in the AP to the plurality of TIM STAs.
[0248] Meanwhile, upon receipt of a frame with an EOSP field set to
1 from the AP, a TIM STA may switch from the awake state to the
doze state.
[0249] In this manner, the TIM STAs' request of UL data or
triggering of a service period by UL MU random access may be
supported by exchanging a frame triggering UL MU random access of
the TIM STAs (e.g., a UL MU Poll Request frame), UL MU random
access-based response frames (e.g., UL MU Poll Response frames) of
the TIM STAs, and an ACK for the UL MU random access of the TIM
STAs (e.g., a UL MU Poll Confirm frame or a block ACK frame).
Herein, because the UL MU Poll Confirm frame or the block ACK frame
does not include information triggering UL MU PPDU transmission of
the plurality of TIM STAs, the TIM STAs may not perform the UL MU
PPDU transmission in response to the UL MU Poll Confirm frame or
the block ACK frame.
[0250] FIG. 21 depicts AC-based UL MU random access according to
the present disclosure.
[0251] To acquire a TXOP for starting a UL MU transmission
procedure, the AP may perform a backoff procedure. For example,
after determining that a channel is idle by sensing the channel
during a PIFS, DISF, or AIFS[i], the AP may select a random backoff
count, wait during a slot time corresponding to the random backoff
count, and attempt to transmit a frame. The random backoff count
may be selected from a range of 0 to CW where CW is a contention
window parameter value. Once the random backoff procedure starts,
the AP activates a backoff timer according to the determined
backoff count. If the channel is idle during a slot time (e.g.,
aSlotTime), the AP may decrement the backoff count by 1 each time.
If the channel is monitored as busy, the AP discontinues the
count-down and waits. If the medium is idle, the AP resumes the
remaining count-down. If the backoff timer reaches 0, the AP may
transmit a frame (e.g., a poll frame triggering UL MU transmission
or a UL MU Poll Request frame).
[0252] An AIFS may be determined according to the AC of the backoff
procedure. The AC may be determined to be one of AC_VO (Access
Category Voice), AC_VI (Access Category Video), AC_BE (Access
Category Best Effort), and AC_BK (Access Category Back Ground).
[0253] In the present disclosure, the AC of a backoff procedure for
transmission of a UL MU Poll Request frame is a primary AC. A frame
triggering UL MU random access (e.g., a UL MU Poll Request frame)
may include primary AC information (or a primary AC field) as
response condition information. Accordingly, STAs having traffic
corresponding to an AC indicated by the primary AC information
included in the frame triggering UL MU random access (e.g., the UL
MU Poll Request frame) among a plurality of STAs may transmit UL MU
random access-based response frames (e.g., UL MU Poll Response
frames). That is, it may be said that UL MU random access is
triggered by the frame triggering UL random access for the STAs
having traffic corresponding to the AC indicated by the primary AC
information among any STAs. Further, the UL MU random access-based
response frames (e.g., the UL MU Poll Response frames) may include
information indicating the AC of the STAs participating in the UL
MU random access (i.e., primary AC information). Therefore, the AP
may determine whether the STAs having traffic corresponding to the
primary AC set when the UL MU random access was triggered has
performed UL MU random access and may determine STAs whose UL MU
transmission is to be triggered.
[0254] A frame triggering UL MU transmission (e.g., a UL MU Poll
Confirm frame) may include primary AC information. Accordingly,
STAs having traffic corresponding to an AC indicated by the primary
AC information included in the frame triggering UL MU transmission
(e.g., the UL MU Poll Confirm frame) may perform the UL MU
transmission. That is, it may be said that UL MU transmission is
indicated to STAs having traffic corresponding to the AC indicated
by the primary AC information by the frame triggering UL MU
transmission. Further, the UL MU transmission (e.g., UL MU PPDU
transmission) may include information indicating the AC of traffic
transmitted in UL MU.
[0255] In the example of FIG. 21, it is assumed that an AC (i.e., a
primary AC) used for the AP to transmit a UL MU Poll Request frame
is AC_VO. In other words, the primacy AC information of the UL MU
Poll Request frame may be set to a value corresponding to AC_VO.
Among STAs receiving the UL MU Poll Request frame, only STAs having
traffic corresponding to AC_VO indicated by the primary AC
information (e.g., STA1, STA2, STA3, and STA4) may transmit UL MU
Poll Response frames to the AP by UL MU random access. Primary AC
information included in the UL MU Poll Response frames may also be
set to a value indicating AC_VO. Therefore, the AP may request or
indicate STA1, STA2, STA3, and STA4 to transmit traffic
corresponding to AC_VO by transmitting a UL MU Poll Confirm frame
triggering UL MU transmission of STA1, STA2, STA3, and STA4.
Primary AC information included in the UL MU Poll Confirm frame may
also be set to a value indicating AC_VO. Therefore, traffic
transmitted in a UL MU PPDU elicited by the UL MU Poll Confirm
frame by each STA may be confined to traffic corresponding to
AC_VO.
[0256] Additionally, UL MU transmission efficiency may be increased
by not limiting UL MU random access or UL MU transmission to a
specific AC. For example, if primary AC information included in a
UL MU Poll Request frame, a UL MU Poll Response frame, and a UL MU
Poll Confirm frame is set to a specific value other than the values
indicating AC_VO, AC_VI, AC_BE, and AC_BK, it may be considered
that there is no constraint on an AC for UL MU random access or UL
MU transmission (i.e., UL MU random access or UL MU transmission is
allowed for traffic corresponding to any AC).
[0257] If the primary AC information of a UL MU Poll Request frame
is set to a specific value other than the values indicating AC_VO,
AC_VI, AC_BE, and AC_BK, STAs having traffic to be transmitted to
the AP may transmit UL MU Poll Response frames irrespective of the
ACs of the traffic. In addition, if the primary AC information of a
UL MU Poll Confirm frame is set to a specific value other than the
values indicating AC_VO, AC_VI, AC_BE, and AC_BK, STAs whose UL MU
transmission is triggered by the UL MU Poll Confirm frame may
transmit traffic having any ACs in a UL MU PPDU to the AP.
[0258] Further, UL MU transmission efficiency may be increased by
enabling STAs whose UL MU transmission is triggered to determine
whether to perform the UL MU transmission before starting to
transmit a UL MU PPDU. For example, STAs receiving a UL MU Poll
Confirm frame may perform virtual carrier sensing (e.g., NAV
check). Only when a channel is idle, the STAs may transmit the UL
MU PPDU. On the contrary, if a virtual sensing result of an STA
receiving the UL MU Poll Confirm frame indicates a channel idle
state, the STA may not participate in transmission of the UL MU
PPDU. This is because even though a carrier sensing result of the
AP indicates a channel idle state, carrier sensing results of STAs
for which UL MU transmission is triggered by the AP may not
indicate the channel idle state. If an STA performs UL MU
transmission even though a carrier sensing result of the STA
indicates a channel busy state, the transmission of the STA may
collide with transmission of another STA currently occupying the
channel. Therefore, only when a virtual carrier sensing result of
each of STAs receiving a frame triggering UL MU transmission (e.g.,
a UL MU Poll Confirm frame) indicates a channel idle state (e.g., a
NAV value is not a non-zero value), the STA may determine that it
can perform the UL MU transmission.
[0259] Now, a description will be given of a method for indicating
or determining a different UL transmission scheme according to
information included in a trigger in trigger-based UL
transmission.
[0260] UL transmission schemes may be classified into UL SU
transmission in which one STA transmits a frame to an AP during a
specific time period, and UL MU transmission in which a plurality
of STAs simultaneously transmit frames to an AP during a specific
time period, according to the number of users participating in UL
transmission. UL transmission schemes may also be classified into
control frame transmission (e.g., transmission of a CTS frame, an
ACK frame, or a PS-Poll frame), data frame transmission, and
management frame transmission (e.g., transmission of an Association
Response frame, a Reassociation Response frame, or a Probe Response
frame), according to the type of a transmitted MAC frame.
[0261] According to the present disclosure, a UL transmission
scheme may be determined according to the type of a trigger in
trigger-based UL transmission. For example, a first-type trigger
frame may elicit a UL MU control frame (e.g., MU CTS), a
second-type trigger frame may elicit a UL SU control frame (e.g.,
SU CTS), a third-type trigger frame may elicit UL MU transmission
(e.g., transmission of UL MU data frames), and a fourth-type
trigger frame may elicit UL MU random transmission.
[0262] More specifically, the type of a response frame may be
determined according to a version of the response frame requested
by a trigger frame, the number of STAs to participate in
transmission of the response frame, and whether an STA to
participate in transmission of the response frame is specified, in
trigger-based UL transmission.
[0263] For example, different types of response frames may be
transmitted for a first version and a second version as versions of
a response frame requested by a trigger frame. Specifically, the
first version may be an older version than the second version. More
specifically, a first-version response frame may be a response
frame conforming to a legacy PPDU format (e.g., a PPDU format
defined by the IEEE 802.11 a/b/g/n/ac standard, for example, a
non-HT PPDU format), and a second-version response frame may be a
response frame conforming to the afore-described HE PPDU
format.
[0264] Further, if the trigger frame requests a first-version
response frame, a different type of response frame may be
transmitted depending on whether the trigger frame indicates one
STA or one or more STAs. If the trigger frame indicates a
first-version response frame from one STA, the indicated one STA
may transmit a first-version UL response frame (e.g., a UL SU
control frame, specifically a legacy CTS (or SU CTS) frame). On the
other hand, if the trigger frame indicates first-version response
frames from one or more STAs, the indicated one or more STAs may
simultaneously transmit first-version UL response frames (e.g., UL
MU control frames, specifically MU CTS frames) simultaneously. That
is, a trigger frame eliciting transmission of first-version UL
response frames from one or more STAs is referred to as a
first-type trigger frame, and a trigger frame eliciting
transmission of a first-version UL response frame from one STA is
referred to as a second-type trigger frame. For example, the
first-type trigger frame may correspond to a UL MU Poll Confirm
frame, and first-version UL response frames that a plurality of
STAs transmit simultaneously in response to the first-type trigger
frame may correspond to legacy CTS frames. The second-type trigger
frame may correspond to a frame requesting transmission of a CTS
frame from one STA and a first-version UL response frame
transmitted in response to the second-type trigger frame by the one
STA may correspond to a legacy CTS frame.
[0265] Meanwhile, if the trigger frame requests a second-version
response frame, a different type of response frame may be
transmitted depending on whether the trigger frame indicates one or
more STAs (e.g. whether the trigger frame implicitly or explicitly
indicates resources for one or more STAs) or whether the trigger
frame indicates no STA (e.g., whether the trigger frame does not
indicate resources for one or more STAs). If the trigger frame
indicates second-version response frames from one or more STAs, the
indicated one or more STAs may participate in UL MU transmission
(e.g., transmission of UL MU data frames) using resources indicated
by the trigger frame. If the trigger frame indicates a
second-version response frame without indicating any STA, one or
more STAs receiving this trigger frame may participate in UL MU
transmission using resources for random access (i.e., resources
allowing collision between transmissions of the one or more STAs).
That is, a trigger frame eliciting transmission of second-version
UL response frames from one or more STAs is referred to as a
third-type trigger frame, and a trigger frame eliciting random
access-based transmission of second-version UL response frames from
one or more STAs is referred to as a fourth-type trigger frame. For
example, the third-type trigger frame may correspond to a UL MU
Poll Confirm frame, and second-version UL response frames
transmitted simultaneously in response to the third-type trigger
frame by a plurality of STAs may correspond to a UL MU PPDU frame.
The fourth-type trigger frame may correspond to a UL MU Poll
Request frame requesting random access of any STA, and a
second-version UL response frame transmitted in response to the UL
MU Poll Request frame by the STA may correspond to a UL MU Poll
Response frame.
[0266] For example, STAs which have received a poll frame
triggering UL MU transmission (e.g., a UL MU Poll Confirm frame)
may provide NAV information around them in order to protect a
channel for transmission of a UL MU PPDU from a third-party STA
(e.g., an STA of an Overlapping BSS (OBSS), a legacy STA, etc.)
that does not listen to the UL MU PPDU. For this purpose, the STAs
may transmit CTS frames. These CTS frames may be transmitted in a
legacy PPDU (e.g., a NON-HT PPDU or a NON-HT duplicate PPDU) so
that all third-party STAs may receive the CTS frames. In this
manner, UL MU transmission efficiency can be increased in an OBSS
environment by allowing adjacent OBSS STAs to set a NAV value using
a trigger-based CTS frame.
[0267] If a plurality of STAs transmit CTS frames simultaneously
based on a trigger, these CTS frames may correspond to MU CTS
frames, and a trigger frame triggering the MU CTS frames may
correspond to as an MU RTS frame. If one STA transmits a CTS frame
based on a trigger, this CTS frame may correspond to an SU CTS
frame and a trigger frame eliciting an SU CTS frame may correspond
to an SU RTS frame
[0268] In addition, CTS frames that STAs transmit in response to a
poll frame triggering UL MU transmission (e.g., a UL MU Poll
Confirm frame) may be CTS-to-Self frames (i.e., CTS frames each
including an RA set to the MAC address of an STA itself).
[0269] To allow third-party STAs to successfully receive CTS frames
corresponding to legacy PPDUs transmitted simultaneously by a
plurality of STAs, MPDUs (i.e., CTS frames) included in PSDUs
transmitted by the plurality of STAs may carry the same contents.
For example, the same scrambling sequence used for PSDU encoding
may be set for all of the plurality of CTS frames. Further, to
include the same information in the plurality of CTS frames, the RA
fields of the CTS frames may be set to the same value (e.g., the
BSSID of the AP), unlike CTS-to-Self frames. In addition, the Frame
Control fields, the Duration fields, etc. of the CTS frames may be
set to the same values.
[0270] FIG. 22 depicts an exemplary trigger type-based UL
transmission scheme according to the present disclosure.
[0271] In the example of FIG. 22, the AP may transmit a UL MU Poll
Request frame through a random backoff procedure. Among STAs
receiving the UL MU Poll Request frame, a plurality of STAs (e.g.,
STA1, STA2, STA3, and STA4) having traffic corresponding to AC_VO
indicated by primary AC information may transmit UL MU Poll
Response frames to the AP. Upon receipt of the UL MU Poll Response
frames from the plurality of STAs, the AP may request or indicate
UL MU transmission to STA1, STA2, STA3, and STA4 by a UL MU Poll
Confirm frame.
[0272] If the UL MU Poll Confirm frame is a first type (e.g., MU
RTS), STA1, STA2, STA3, and STA4 may configure and transmit CTS
frames (e.g., CTS-to-Self frames) in a legacy PPDU format before
starting to transmit a UL MU PPDU. In this manner, the plurality of
STAs may transmit a UL MU PPDU including traffic corresponding to
AC_VO an SIFS after transmitting the MU CTS frames
simultaneously.
[0273] As illustrated in FIG. 22, the transmission times (or
lengths) of a plurality of CTS frames may be set to the same value.
For this purpose, the seed value of the scrambling sequence, MCS,
or rate of a trigger frame (e.g., a UL MU Poll Confirm frame or an
MU RTS frame) triggering the plurality of CTS frames that are
transmitted simultaneously may be used commonly for transmission of
the plurality of CTS frames.
[0274] Additionally, transmission of a CTS frame (i.e., an SU CTS
frame) from one STA may be elicited by a trigger frame. For
example, if the UL MU Poll Confirm frame is a second type (e.g., SU
RTS), one of the plurality of STAs may transmit a SU CTS frame.
[0275] As described above, a trigger frame requesting CTS frames
before transmission of a UL MU PPDU starts may be directed to a
plurality of STAs requested for UL MU PPDU transmission (i.e., a
first-type trigger frame) or one of STAs requested for UL MU PPDU
transmission (i.e., a second-type trigger frame).
[0276] Additionally, UL MU data transmission from a plurality of
STAs may be elicited by a trigger frame. For example, if the UL MU
Poll Confirm frame is the third type, a plurality of STAs may
transmit data frames in UL MU. As illustrated in the example of
FIG. 22, a plurality of STAs may be requested to transmit a UL MU
PPDU in immediate response to a trigger frame (e.g., immediately an
SIFS after reception of the trigger frame), rather than they are
requested to transmit CTS frames before they start to transmit a UL
MU PPDU.
[0277] Also, UL random access transmission from one or more STAs
may be elicited by a trigger frame. For example, if the trigger
frame is the fourth type like a UL MU Poll Request frame, an STA
may transmit a UL MU Poll Response frame in random access allowing
collision.
[0278] In this manner, the AP may request or indicate different
types of UL transmission using a trigger frame (e.g., a UL MU Poll
Confirm frame). That is, one of MU CTS transmission, SU CTS
transmission, UL MU PPDU transmission, and UL random access
transmission may be performed according to information included in
a trigger frame.
[0279] For this purpose, explicit information indicating the type
of a trigger frame may be included in the trigger frame so that a
UL transmission scheme may be determined based on the information.
Or trigger frame types corresponding to trigger frames of a
plurality of formats are preset so that when a trigger frame of a
specific format is received, a UL transmission scheme may be
determined according to a trigger frame type corresponding to the
format.
[0280] Or a new field indicating whether CTS transmission is
requested may be added to a trigger frame. Thus, whether a CTS
frame is to be transmitted before transmission of a UL MU PPDU may
be indicated. Or information indicating the type of a CTS frame
(e.g., information indicating MU CTS or SU CTS) may be added to a
trigger frame. If the information does not indicate any CTS type
(or the information is reserved), a UL MP PPDU may be transmitted,
not preceded by a CTS frame. Or a field indicating whether CTS
transmission is requested and information indicating a CTS type
(e.g., information indicating MU CTS or SU CTS) may be added to a
trigger frame.
[0281] FIG. 23 depicts an exemplary method according to the present
disclosure.
[0282] In step S2310, an AP may transmit a first trigger frame to
an STA group (i.e., an STA group including one or more STAs). For
example, the first trigger frame may correspond to a poll frame
triggering UL MU transmission or a UL MU Poll Request frame for UL
MU random access.
[0283] In step S2320, each STA of the STA group may determine
whether to respond to the first trigger frame based on information
included in the first trigger frame. For example, if the first
trigger frame corresponds to a poll frame triggering UL MU
transmission and includes information requesting UL MU transmission
to the STA receiving the poll frame, the STA may determine to
perform first UL MU transmission in response to the first trigger
frame. Or if the first trigger frame corresponds to a UL MU Poll
Request frame for UL MU random access, the STA receiving the UL MU
Poll Request frame may determine whether to participate in UL MU
random access based on whether a response condition for the UL MU
random access is satisfied.
[0284] An STA that has determined to respond to the first trigger
frame in step S2320 may perform the first UL MU transmission. For
example, if the first trigger frame corresponds to a poll frame
triggering UL MU transmission, the first UL MU transmission may
correspond to transmission of a UL MU PPDU including UL frames from
a plurality of STAs. Or if the first trigger frame corresponds to a
UL MU Poll Request frame for UL MU random access, the first UL MU
transmission may include a UL random access-based UL MU Poll
Response frame. The UL random access-based UL MU Poll Response
frame may include information indicating that the STA transmitting
the UL random access-based UL MU Poll Response frame will
participate in UL MU transmission. Or if the STA transmitting the
UL random access-based UL MU Poll Response frame is a TIM STA, the
UL random access-based UL MU Poll Response frame may include
information requesting DL data transmission.
[0285] In step S2330, transmissions from all STAs participating in
the first UL MU transmission from the STA group may end at the same
time point indicated by the first trigger frame. For this purpose,
one or more of the STAs participating in the first UL MU
transmission may add paddings to their transmitted UL frames.
[0286] In step S2340, upon receipt of a UL frame from at least one
STA of the STA group performing the first UL MU transmission, the
AP may determine that frame exchange initiated by the first trigger
is successful. Also, upon receipt of a UL frame without an error
from at least one STA of the STA group performing the first UL MU
transmission, the AP may determine to transmit a response frame to
the first UL MU transmission.
[0287] In step S2350, the AP may transmit a DL MU frame to the STA
group in response to the first UL MU transmission. The DL MU frame
may include at least one of a plurality of units for the plurality
of STAs and an additional trigger frame (e.g., a second trigger
frame). Each of the units for the plurality of STAs may include at
least one of ACK information (e.g., a block ACK frame) for UL
transmission from one of the plurality of STAs participating in the
first UL MU transmission and a DL data unit for one of the
plurality of STAs. In an embodiment, the DL MU frame may include
block ACK information for the plurality of STAs and a second
trigger frame. The ACK information or the second trigger frame that
the AP transmits in response to the first UL MU transmission may be
transmitted a specific IFS (e.g., an SIFS) after the ending time of
the first UL MU transmission (i.e., the ending time of the first UL
MU transmission, indicated by the first trigger frame). Also, the
ACK information for the first UL MU transmission and the second
trigger frame may be included in one frame and thus simultaneously
transmitted. If the first UL MU transmission includes information
requesting DL data transmission from TIM STAs, the AP may transmit
DL data in response to the information. The DL data may be
transmitted in a DL MU PPDU to a plurality of TIM STAs.
[0288] In step S2360, only when the frame transmitted in response
to the first UL MU transmission by the AP in step S2350 includes a
second trigger frame, second UL MU transmission may be performed.
That is, an STA that has received the second trigger frame in step
S2350 may determine whether UL MU transmission is requested to the
STA. If UL MU transmission is requested to the STA, the STA may
participate in the second UL MU transmission.
[0289] FIG. 24 depicts another exemplary method according to the
present disclosure.
[0290] In step S2410, an AP may transmit a trigger frame to an STA
group (i.e., an STA group including one or more STAs). The trigger
frame may be a first, second, third, or fourth type. Explicit
information indicating the type of the trigger frame may be
included in the trigger frame, or the type of the trigger frame may
be implicitly indicated according to a predetermined format. Also,
the trigger frame may be a first or second trigger frame in the
example of FIG. 23.
[0291] In step S2420, upon receipt of the trigger frame, an STA may
determine whether to respond to the trigger frame by NAV check. For
example, if the STA determines that a channel is busy by the NAV
check (e.g., a NAV value is a non-zero value), the STA may not
respond to the trigger frame in step S2430. Or if the STA
determines that the channel is idle by the NAV check (e.g., the NAV
value is not a non-zero vale), the STA may determine to respond to
the trigger frame in step S2440.
[0292] In step S2440, the STA receiving the trigger frame may
determine whether the trigger frame requests a first-version
response frame or a second-version response frame. The first
version may be an older version than the second version. More
specifically, the first version may correspond to a legacy PPDU
format such as a non-HT version, and the second version may
correspond to a HE PPDU format. If the first-version response frame
is requested, the STA proceeds to step S2450 and otherwise, the STA
may proceed to step S2460.
[0293] In step S2450, if the trigger frame indicates one STA, the
one STA may transmit a first-version response frame in step S2451.
If the trigger frame indicates one STA and does not include
resource allocation information, the one STA may transmit the
first-version response frame. In this case, the trigger frame
corresponds to the afore-described second-type trigger frame. The
STA indicated by the second-type trigger frame may transmit the
first-version response frame (e.g., an SU legacy control frame,
specifically a legacy CTS frame) elicited by the second-type
trigger frame in UL SU.
[0294] If the trigger frame indicates one or more (e.g., a
plurality of) STAs, not just one STA in step S2450, the one or more
STAs may transmit first-version response frames in step S2452, as
illustrated from exchange between a UL MU Poll Confirm frame and a
CTS frame in FIG. 22. If the trigger frame indicates one or more
STAs and does not include resource allocation information, the one
or more STAs may transmit first-version response frames. In this
case, the trigger frame corresponds to the afore-described
first-type trigger frame. Also, the first-type trigger frame may be
multicast or broadcast. If the first-type trigger frame is
multicast, the first-type trigger frame may indicate one group of
STAs. If the first-type trigger frame is broadcast, the first-type
trigger frame may indicate all STAs receiving the trigger frame.
The one or more STAs indicated by the first-type trigger frame may
simultaneously transmit first-version response frames (e.g., MU
legacy control frames, specifically MU CTS frames) elicited by the
first-type trigger frame in UL MU transmission. The whole or part
of the first-version response frames may be transmitted in the same
resources corresponding to shared resources. The same resources may
refer to partially or fully identical time, frequency, and space
resources.
[0295] On the other hand, if the trigger frame indicates one or
more STAs (e.g., dedicated resources are explicitly or implicitly
allocated for UL transmission of one or more STAs) in step S2460,
the one or more STAs may transmit second-version response frames in
the allocated resources as illustrated from exchange between a UL
MU Poll Confirm frame and a UL MU PPDU frame in FIG. 21, in step
S2461. In this case, the trigger frame corresponds to the
afore-described third-type trigger frame. The one or more STAs may
simultaneously transmit second-version response frames (e.g., UL MU
frames, specifically UL MU data frames) elicited by the third-type
trigger frame in UL MU transmission.
[0296] If the trigger frame does not indicate one or more STAs and
allows transmission of an STA unspecified by the AP in step S2460,
one or more unspecified STAs may transmit second-version response
frames as illustrated from exchange between a UL MU Poll Request
frame and a UL MU Poll Response frame in FIGS. 18 and 19, in step
S2462. The one or more STAs may participate in UL MU transmission
using random access resources allowing collision. In this case, the
trigger frame corresponds to the afore-described fourth-type
trigger frame. The one or more STAs may simultaneously transmit
second-version response frames (e.g., UL MU frames, specifically UL
MU data frames) elicited by the fourth-type trigger frame using
random access resources allowing collision.
[0297] As described above, a different UL transmission scheme or a
different UL transmission frame type may be determined according to
the type of a trigger frame.
[0298] While the exemplary method has been described with reference
to FIG. 23 or FIG. 24 as a series of operations for simplicity of
description, this does not limit the sequence of steps. When
needed, steps may be performed at the same time or in a different
sequence. All of the exemplary steps are not always necessary to
implement the method proposed by the present disclosure.
[0299] The foregoing embodiments of the present disclosure may be
implemented separately or combinations of two or more of the
embodiments may be implemented simultaneously, for the method of
FIG. 23 or FIG. 24.
[0300] The present disclosure includes an apparatus for processing
or performing the method of the present disclosure (e.g., the
wireless device and its components described with reference to
FIGS. 1, 2, and 3).
[0301] The present disclosure includes software (an operating
system (OS), an application, firmware, a program, etc.) for
executing the method of the present disclosure in a device or a
computer, and a medium storing the software that can be executed in
a device or a computer.
[0302] While various embodiments of the present disclosure have
been described in the context of an IEEE 802.11 system, they are
applicable to various mobile communication systems.
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